PM_2.5, a main particulate air pollutant, poses a serious hazard to human health. The exposure to PM_2.5 increases mortality and morbidity of many respiratory diseases such as asthma, chronic obstructive pulmonary diseases and even lung cancer. The contribution of reactive oxygen species (ROS) in the PM_2.5-induced acute lung injury process was confirmed in our previous research, but the molecular mechanism based for it remains unclarified. In this research, ROS-induced lung injury after exposure to PM_2.5 was explored in vivo and in vitro. The in vivo study indicated that N-acetyl-L-cysteine (NAC) could attenuate the accumulation of inflammatory cells, the thickening of alveolar wall and the degree of lung injury. Furthermore, we found ROS could regulate the intracellular Ca²⁺ level, expression of the Transient Receptor Potential Melastatin 2 (TRPM2), NLRP3 and its downstream inflammatory factors in vivo. In vitro experiments with A549 cells and primary type II alveolar epithelium cells (SD cells) showed that ROS induced by PM_2.5 exposure could mediate intracellular Ca²⁺ mobilization via TRPM2, with a subsequent activation of NLRP3. In our present study, we demonstrated the contribution of the ROS-TRPM2-Ca²⁺-NLRP3 pathway in PM_2.5-induced acute lung injury and offered a potential therapeutical target valid for related pathology.