To explore whether vitamin B complex (folic acid, B6 and B12) can inhibit the acute lung injury of PM_2.5 in rats, the authors randomly divided 56 SD rats into control group, different doses (0.4, 2.0, 10.0 mg/mL) of PM_2.5 exposure groups and corresponding vitamin B complex intervention groups (0.02 mg/mL folic acid, 1 mg/mL vitamin B₆, 0.002 5 mg/mL vitamin B₁₂). The lung tissue of rats was taken for HE staining to observe histopathological changes and calculate pathological scores. The bronchoalveolar lavage fluid (BALF) was collected to determine the content of total protein (TP), lactate dehydrogenase (LDH), alkaline phosphatase (AKP), acid phosphatase (ACP), malondialdehyde (MDA), superoxide dismutase (SOD) and Catalase (CAT). The results showed that PM_2.5 exposure could cause different degrees of pathological damages of lung tissue in rats, and vitamin B complex could alleviate those damages. Compared with the control group, the content of LDH, AKP, ACP, TP and MDA in BALF of low, medium and high dose of PM_2.5 groups significantly increased (P<0.05), while the activity of SOD and CAT significantly decreased (P<0.05). The content of TP and MDA increased with the increase of PM_2.5 doses (P<0.05). The content of LDH, TP and MDA significantly decreased in the intervention groups of three PM_2.5 doses (P<0.05), while SOD and CAT activity significantly increased (P<0.05). The content of ACP was significantly reduced in BALF in low and high dose of PM_2.5+vitamin B complex groups (P<0.05). There was no significant change in ACP content in BALF in the medium dose of PM_2.5+vitamin B complex group. Only the low dose of PM_2.5+vitamin B complex group exhibited a decrease in AKP content (P<0.05), and the other intervention groups showed no significant change in AKP content. Therefore, it is held that PM_2.5 could break the pulmonary oxidation-antioxidant balance to cause acute lung injury in rats, while vitamin B complex could alleviate the damage to protect the body.