The invention discloses a fluid power machine which comprises a hollow shaft, an output shaft, blade shaft brackets, blade shafts, main drive blades, a sleeve, a rudder plate and a rudder plate direction lock device. Each blade shaft is meshed with a movable rack arranged on the blade shaft brackets through a blade drive gear; a rudder plate hinge element is fixedly connected with a cam; two cam drive pins fixedly connected with the movable rack are arranged on the wheel face of the cam, and a balance plate arranged at one side of the rudder plate is fixedly connected with the rudder plate hinge element. Compared with the prior art, the power machine has the advantages of small transmission impact, stable operation, high reliability, more rational structure, convenience for manufacture, installation and maintenance, longer service life, simple and reliable lock blade structure and more accurate direction location of the fluid, and the effective utilization rate of fluid power and the power of the power machine can ne improved.