Abstract: Based on related theory of fulid mechanics, we builds decompressor mathematical model of Biopak240R positive pressure orygen respirator in operation process, and analyzes the impact of decompressor stability and main structural parameters on its key performance parameters. The results show that decompressor has better stability; the outlet pressure and flow rate of decompressor is proportional to spring stiffness and valve core diameter of outlet cavity and inversely proportional to valve core diameter of control cavity, the main factors of all parameters are sorted valve core diameter of outlet cavity, valve core diameter of control cavity, spring stiffness in descending order.