A pneumatic ratchet wrench is connected with an air supply device and contains: a housing, a ratchet head unit, an impact clutch unit, and a driving unit. The housing extending along a first axis line and includes an opening defined on a front end thereof and an intake formed on a distal end thereof so as to couple with an air supply device. The ratchet head unit is received in the housing and includes a drive square extending along a second axis line and extending out of the opening The impact clutch unit is received in the housing and is coupled with the ratchet head unit. The driving unit is disposed in the housing and includes a multi-chamber cylinder, a rotor member inserted into the multi-chamber cylinder and connecting with the impact clutch unit. The multi-chamber cylinder has a body, a first chamber, and a second chamber communicating with the first chamber.