A multistage pneumatic motor includes a shell (1) and a power output main shaft (2). The shell (1) is provided with a gas inlet (3) and a gas outlet (4). Two or more pneumatic motor stages (11, 12, 13) are installed in the shell (1). The first pneumatic motor stage is communicated with the gas inlet (3), and the last pneumatic motor stage is communicated with the gas outlet (4). Compressed gas enters the shell (1) through the gas inlet (3), drives the first pneumatic motor stage, then drives the next pneumatic motor stage, and is exhausted from the shell (1) through the gas outlet (4) at last. Every pneumatic motor stage is provided with a power output shaft (112, 122, 132) which is connected to the power output main shaft (2), so that the powers produced by all pneumatic motor stages (11, 12, 13) are jointed together and then output by the power output main shaft (2). The multistage pneumatic motor improves working efficiency greatly, saves energy source and reduces noise.