The battle began before the dawn of 17 February by a Chinese artillery barrage against Vietnamese positions. The first objectives for the PLA were the towns of Bát Xat, Muong Khuong, and Pha Long. 20,000 troops from the PLA 13th Army crossed the Red River into Bat Xat using pontoon bridges, quickly overrunning the Vietnamese defense held by the VPA 192nd Regiment, as well as the independent 2nd and Lào Cai Battalions. No attack was staged against Phong Thð on the first day.

The brunt of Chinese assaults fell on the VPA 345th Division, which resisted toughly. Two Chinese regiments were held off at Mðng Xðn and in the area south of Chu Dang and west of Nhoc Son, which forced the PLA to change their plan into a mop-up operation against the Vietnamese strongholds. By the dusk of 18 February, the Vietnamese defenders in Bao Thang and Côc Lê?u had been completely encircled. At 14:00 on 19 February, the PLA captured Lao Cai City. In response to the loss of the provincial capital, the VPA 345th Division command sent one battalion from its 118th Regiment to reinforce its 121th Regiment's positions at Coc Tha, Dien Na, Dung Ha and Chan Uy, while the VPA 316th Division was mobilized eastward to Sapa.

Having taken Lao Cai, the PLA then sent troops, presumably from the 13th Army, to Cam Duong to the south, and another group (probably from the 14th Army) advancing along Highway 4D to Sapa, which was 38 km to the southwest. The Kunming Military Region Command used fresh elements from the 149th Division and the 11th Army to reinforce the 13th Army in the efforts against Cam Duòng. A blocking position was established by four companies from the PLA 39th Division of the 13th Army on Highway 10 at Thay Nai to cut the VPA 345th Division from supply. The VPA 316th Division was then dispatched from Sapa to meet the approaching Chinese forces, and ran into contact on the secondary road between Lao Cai and Sapa on 22 February. From 22 to 25 February, its 148th Regiment launched repetitive attacks against the Chinese block at Thay Nai, but failed to break through and secure its way to Cam Duòng. Two PLA divisions from the 13th Army, the 37th and 38th, were deployed against the VPA 345th Division, which was defending a narrow area north of Cam Duong. By 25 February, the Chinese had seized Cam Duong, yet were still struggling to exterminate pockets of Vietnamese resistance in Lao Cai and other towns under their control, a situation which had not ended until 27 February.

On 24 February, the PLA decided to supplement their reserves, the 149th Division, to the fight against the VPA 316th Division. Chinese efforts now concentrating on cutting off the retreat of the VPA 316th Division, as the PLA 447th Regiment skirted around Mount Phan Xi Pang through the Hoang Lien Son Pass and maneuvered toward the direction of Bình Lu, which was 44 km west of Sapa. In meantime, the rest of the 149th Division pushed toward Sapa along two roads parallel to Highway 10. Despite showing excellent combat performance, the VPA 316th Division was finally forced to retreat due to the lack of manpower. At 14:45 on 1 March, Sapa fell to the PLA. On the eastern wing of the offensive, Khoc Tiam succumbed to a night assault raging from 20:00 on 2 March to 14:45 on 3 March. At 19:00 on 3 March, all roads that connected Phong Tho with Binh Lu and Pa Tan had been under Chinese control. On 4 March, Chinese forces eventually captured the town, thus successfully blocking the supply route to the VPA 316th Division from Lai Chau; the blocking position was at least 40 km from the Sino-Vietnamese border, becoming the deepest Chinese penetration in the war. The 316th Division finally ceased fighting on 5 March. On the same day, the Chinese government announced the withdrawal of troops from Vietnam