Objective To explore the effect of P22phox on human pulmonary artery smooth muscle cells (HPASMCs) induced by hypoxia and its possible mechanism. Methods HPASMCs were cultured under normoxia or hypoxia in vitro. HPASMCs were randomly divided into blank control group, si-NC+oe-NC group, si-P22phox+oe-NC group and si-P22phox+oe-KLF4 group, The cells are transfected according to the grouping and then cultured under hypoxia. CCK-8 experiment was used to detect cell viability. EdU experiment was used to detect cell proliferation ability. Cell scratch experiment was used to detect cell migration. Transwell experiment was used to detect cell migration. qRT-PCR and Western blot were used to detect the expression of P22phox and KLF4 in cells. Results Compared with the normoxic group, the cell viability, EdU+ cell number, scratch healing rate and number of migrating cells in the hypoxia group were significantly increased (P＜0.05), and the expression of P22phox and KLF4 mRNA and the expression of P22phox and KLF4 protein were significantly increased (P＜0.05). Compared with the blank control group, the si-NC+oe-NC group had no significant difference in cell indicators (P＞0.05). Compared with the si-NC+oe-NC group, the expression of P22phox and KLF4 mRNA in si-P22phox+oe-NC group was significantly reduced (P＜0.05), the expression of P22phox and KLF4 protein was significantly reduced (P＜0.05), cell viability, EdU+ cell number, scratch healing rate and number of migrating cells were significantly reduced (P＜0.05). Compared with the si-P22phox+oe-NC group, the expression of P22phox mRNA and protein in the si-P22phox+oe-KLF4 group was not statistically different (P＞0.05), while the expression of KLF4 mRNA and protein was significantly increased (P＜0.05), cell viability, EdU+ cell number, scratch healing rate and number of migrating cells were significantly increased (P＜0.05). Conclusion P22phox promotes the proliferation and migration of HPASMCs induced by hypoxia by up regulating the expression of KLF4.