A rotary fluid machine includes a cylinder with an annular cylinder chamber, an annular piston and a blade. The annular piston is disposed in the cylinder chamber so as to be eccentric to the cylinder. The annular piston divides the cylinder chamber into an outer cylinder chamber and an inner cylinder chamber. The blade is arranged in the cylinder chambers to divide each of the outer and inner cylinder chambers into a high-pressure chamber and a low-pressure chamber. The cylinder and the piston are arranged to eccentrically move relative to each other. A height of the outer cylinder chamber is different from a height of the inner cylinder chamber as measured in a direction of a rotational axis of the rotary fluid machine.