After capturing the northern heights above Lång So'n, the Chinese surrounded and paused in front of the city in order to lure the Vietnamese into reinforcing it with units from Cambodia. This had been the main strategic ploy in the Chinese war plan as Chinese leader Deng Xiaoping did not want to risk an escalation potentially involving the Soviet Union. The Vietnam People's Army (VPA) high command, after a tip-off from Soviet satellite intelligence, was able to see through the trap, however, and committed reserves only to Hanoi. Once this became clear to the PLA, the war was practically over. An assault was still mounted, but the Vietnamese only committed one VPA regiment defending the city. After three days of bloody house-to-house fighting, Lång So'n fell on 6 March. The PLA then took the southern heights above Lång So'n.

Although the PLA managed to capture and briefly occupy Lång So'n and its nearby vicinities, the campaign was slower and more costly than the Chinese leadership had anticipated, with the PLA's regular units suffering heavy casualties against the guerilla tactics of Vietnamese militia and irregular units.

According to the Washington Post, analysts described the battle as being an important Chinese victory for capturing the Vietnamese capital of Lång So'n. "They beat the hell out of the Vietnamese," stated one analyst in describing the battle around L?ng Son. "The Vietnamese know that; the Russians know that. That is all the Chinese are interested in." Vietnamese resistance being too heavily preoccupied elsewhere near Lao Cai and Cao Bang in the middle of the front was highlighted as a contributing factor to the Vietnamese defeat in Lång So'n. Some Bangkok analysts stated Vietnam was at least successful in keeping their losses low by avoiding direct battles between its Hanoi based main-force units with the Chinese forces.