Why would China fight a war with Australia? But if they ever go to war one on one Australia stands NO chance simple!! Australia is big country but very small population and very small economy vis a vis China. I like Australia and Australians but my sincere advise to them would be Don't start anything with China " You will not win"". Period.
I think you don't understand how expeditionary warfare work.
If and when China start a war (one on one or not) with Australia, China is fighting an expeditionary warfare, across a distant of about 5,000km (give or take), which mean it does not actually matter how many Troops Chinese Military Chinese military have or How many ship the Chinese Navy have, those number did not matter because you cannot bring them all 5,000 km away in a foreign theatre. Only the Troop and Ship China can forward deploy counted.
In this case, it's about logistic, sea/airlift, forward deployable troop and supply. In this stage, if we counted every logistic, sea/airlift capability, China can afford about 1 Brigade Combat Team size force with support element that far (judging by the fact China only have 4 Battalion size LPD (Type 071) and other 30 or so LSD (Type 072, 073, 074) are company size or less, which mean about 7500 (30x150 + 4 x 800) troop strength, which is a US BCT size strength.
Logistic is even less, China have 18 underway replenishment ship (type 091, 093 and 094) which mean these ship were responsible for the whole 10,000 km round trip whatever Chinese Fleet has to made to and from Australia to complete 1 resupply cycle, which mean conventionally, China can only support 15-20% of her naval force that far. So each landing trip Chinese made, have to come all the way from China and by ship, you are talking about a landing frequency of 20-25 days per cycle, which in layman term, even if logistically sustainable, China can put 7000 troop in Australia soil every 20 to 25 days by sea. That is the physical limits.
Airlift Capacity is a bit better but not a lot. With 140 assorted Transport with up to 90 troop in Y-8 and 120 troop in Y-20, the average Airliftable troop China can deploy is about 14,000 ( approximately a division strength) and flight time is about 17 hours round trip, which mean the number China can airlift in or out of Australia is 14,000 per 17 hours (let's call it a day), that is if China can deploy all their transport and guard them at once. However, airlift troop lack of heavy weapon and armoured support and have to be light infantry.
Basically China can put about 14000 troop per day by air and 7000 troop per month by sea before attribution (so the number goes down if the transport was shot down and sunk)
On the other hand, Australia have 70000 active and reserve defence force but can expand with civil defence training to 300,000 (The Military have 300,000 set of equipment for short term training) which mean given training time (which is usually 9 weeks, but usually shorter in emergency) Australia Army can field 300,000 troops in 2 months and a 1 week time. Covering a land as big as China, with population sparse and population center separated, which mean every town is essential to be link up between 2 capital city (eg Wollongong is a strategic important town to link up between Sydney and Melbourne) Which mean Chinese force have to take not only the big population center, but surrounding satellite city in order to keep the MSR between Capital City open.
With number like that, you are needing a lightly armed force to seize and guard both strategically important cities and Captical City, China would have a hard time doing so, even more so, large ground area favour guerrilla warfare, which mean China not only need to face conventional Australian force in Australian soil, but also insurgency in occupying town.
Can China pull this off? Let me give you a for instant, when I was in the US military, I came across of a warplan detailing a full scale invasion of Australia (they do that to EVERY allied country in case they felt to the suggested enemy). The report, which is classified, and which I cannot tell you what's inside, but I can tell you this, US Military would have problem seizing Australia with its current Sea/Airlift capacity, and you are talking about multiple flow in strength in logistic and sea/airlift capacity, and they have American Samoa and Guam (which is closest naval and air base toward Australia and Guam is only 2500 km from Australia) to act as Forward Deployment/staging area.