PLA Invasion force and casualties:
Vietnamese sources suggest an invasion force of 600,000 PLA soldiers entering the country,
this is unfortunately impossible due to logistics. After 25 years of rapid infrastructural development, in 2003, the PLA managed to deploy 300,000 RRF troops to Xinjiang in 3 weeks.
There was simply no way the PLA could've moved 600,000 soldiers with backup troops to the Vietnamese border in 5 weeks in 1979. 
A much more realistic
PLA Invasion force into Vietnam numbered 80,000 with another 150,000 remaining on the Chinese side of the border. This is a number quoted from both internal de-classified PLA sources and
quoted as an estimate from American/Soviet sources via satillite imagery.
Now as for total casualties.
Western Sources estimate a total PLA casualty count of 20,000. PLA indicates 6,900 killed, 15,000 wounded which implies 22,000 total casualties.
Vietnam claims 26,000 PLA troops KIA, 37,000 WIA through the entirety of the war.
The KIA is clearly an exaggeration due to the fact that if this was the case, ~80% of the entire PLA invasion force would've been casualties. The WIA could be more realistic however due the border war lasting for 10 years.
Realistic PLA KIA: ~6900 Total
~6300(1979 invasion)
~200 in Operation LanJianI(1982)
~70 in Operation Laoshan(1984)
~300(1985-1988).
Vietnamese Defending Force:
Vietnam had 100,000 regular army forces along the border during the 1979 invasion. This point is agreed upon by PLA, Western, and Vietnamese forces. What is also agreed upon by all parties is that Vietnam suffered 12,000 regular forces KIA in 1979 and another 8,000 regular forces KIA for the remainder of the border war until 1988.
The PLA asserts that there were an additional 100,000 Vietnamese militia forces during the 1979 campaign, and that 20,000 of these militiamen were KIA. Western sources appear contradictory on the topic with some agreeing and some disagreeing upon that number. Vietnamese sources claims that there were no guerilla militia forces and that the PLA killed 10,000 vietnamese civilians. But then the Vietnamese army also has sources honoring these same civilians for fighting against the PLA during the 1979 invasion. Specifically they have a memorial for the 10,000 people. So at this point it can be asserted that at least 10,000 non uniformed Vietnamese were killed, whether they were civilians or militia or both is up for question.
It can be assumed that the PLA claim of 20,000 militia KIA is an exaggeration. Due to the ambiguity of the sources, I'll simply take the average from the Chinese and Vietnamese claims => 15,000 Vietnamese militia/civilians killed in 1979
Total Vietamese Casualties: ~35,000
~27,000 (12,000 Regular + 17,000 militia/civilian in 1979)
~1000 regulars in 1982
~4000 regulars in 1984
~3000 regulars from 1985-1988
That is an average kill ratio of 1:5 in favor of the PLA. While the PLA did better in the Indian and Tibetan campaigns, this ratio compares very favorably to the PLA's performance in Korea against U.N forces which was 2:1. So while the war with Vietnam exposed many shortcomings of the PLA immediatly after the cultural revolution. In the acheivement of it's overall objectives(took Vietnamese Land,forced even tual vietnamese withdraw from Cambodia+Laos) with such a casualty ratio, one can argue that the PLA didn't do at all too badly with what they had on hand.
