It's basically the only actual combat experience the PRC has in the last 30 years....(unless you count running over unarmed college students with tanks, which I don't.)
And by all accounts their performance was horrible.
They had some pretty good showings against the soviets in the late 60s. Readjusted the border be a few thousand square miles.
After the US left, Vietnam consolidated their control of Laos and Cambodia and leaned towards the Soviet Union (by purging pro Chinese officials in the Vietnamese Communist Party and considered offering Cam Rham Bay as a Soviet naval station). China responded by instigating stone throwing incidents between their border units with Vietnam's border units. China attacked Vietnam to remind her who was the regional power. China mobilized 100,000 front line troops stationed in the southern region and Vietnam responded by defending with milita units (composed of war veterans) as a way of telling the Chinese that their second line troops can beat any front line Chinese troops. The war showed the Chinese leaders how backwards their military was. The PLA lacked modern communications, troop leaders lacked technical military skills because most of their garrison time was spent on studying the Thoughts of Chairman Mao and not military tactics. Officers were promoted based more on their knowledge of Maoist thought than military skills. The Chinese officers relied on set battle plans and were unable to cope when the plans went awry. Initially the Chinese forces would advance into Vietnam, not knowing that they had bypassed Vietnam troops hidden in hilly caves. These troops would come out and attack Chinese reinforcements and convoys. The border area where most of the combat occurred was jungle and hilly with little or no roads. The Chinese had rudimentary logistics (trucks and mules) to bring up supplies but it rapidly broke down because the front line troops were using more ammo than their logistics capability can bring up. Initially the Vietmanese tactic of yielding territory and attacking Chinese rear troops worked but it meant two border provinces would have to fall into Chinese hands. Vietnam ordered their troops to stop the hit and run approach and dig in around the provincal capitals and prepare to fight a fixed battle. That decision allowed the Chinese to bring up their artillery and attack an enemy who was in fixed positions. That was probably one of the decisive mistakes made by the Vietmanese. The destuction of these two towns using old fashion massed artillery forced Vietnam to commit regular forces. Both sides realized that the war was escalating and decided to call for a ceasefire. This is also the war that forced China to realize that the Maoist dogma that the soldiers political motivation is more important than having modern weapons was wrong. The rudimentary Chinese regular infantry troops loss over 10 percent casualties within one month of fighting mainly second line Vietmanese troops (border and militia). Lacking modern command and control, and radios, battle plans degenerated into frontal human wave assualt on Vietmanese positions. This war was a wake up call for the PLA to modernize their forces.