Disclosed are a fluid power conversion apparatus and a conversion method. The apparatus comprises a stator (110), a rotor (120), a separation plate (130) and sliding blocks (140), wherein the rotor (120) and the stator (110) are rotatably connected, and a circular annular cavity (150) is formed between opposing side walls of the rotor (120) and the stator (110); an inlet (111) and an outlet (112) are provided on the stator (110), the separation plate (130) is fixedly connected on the stator (110) and is connected in a slidable manner to the rotor (120), and the separation plate (130) is located in the circular annular cavity (150), between the inlet (111) and the outlet (112). The rotor (120) corresponds to sliding grooves (121) provided on a surface of the circular annular cavity (150), a sliding block (140) is provided in each sliding groove (121), the sliding blocks (140) extend out of the sliding grooves (121) and, together with the separation plate (130), divide the circular annular cavity (150) into two sub-cavities of unequal pressure, and the sliding blocks (140) retract in the sliding grooves (121) to traverse the separation plate (130). The conversion method is based on the conversion apparatus, using fluid pushing sliding blocks (140) to drive the rotor (120) to rotate relative to the stator (110), or an external power being connected to drive the rotor (120) to rotate relative to the stator (110), and the sliding blocks (140) extending from the rotor (120) driving the fluid to flow. The fluid power conversion apparatus and conversion method have a simple structure and high energy conversion efficiency.