A screw expansion power generation device, wherein the power generation device comprises a semi-sealed or fully sealed shell, the shell comprises an expander cavity and a generator cavity; the expander cavity is not in fluid communication with the generator cavity; a screw expander is disposed in the expander cavity, and a generator is disposed in the generator cavity; a rotor of the screw expander is fixedly connected to a rotor of the generator; the power generation device drives the generator to generate power through rotation of the rotor of the screw expander; and a liquid refrigerant injection inlet and a refrigerant outlet are disposed on the generator cavity; the liquid refrigerant injection inlet is disposed on the top of the shell far from the expander cavity, the refrigerant outlet is disposed at the bottom of the shell near to the expander cavity; and the generator is cooled through evaporation of a liquid refrigerant, wherein the screw expander comprises a male rotor and a female rotor, and a shaft of the male rotor is fixedly connected to the rotor of the generator, characterized in that a first male rotor bearing is disposed at an end of the male rotor away from the rotor of the generator, and female rotor bearings are separately disposed at two ends of the female rotor, the male rotor comprises a rotor part and a connection part which are integrally designed, and the rotor part coordinates with the female rotor; the connection part extends into the generator; and the expander cavity and the generator cavity are isolated from each other through an isolation mechanism, so that a hole is formed between the expander cavity and the generator cavity; the connection part passes through the hole and enters the generator cavity, and an end of the connection part away from the rotor part is fixedly connected to the rotor of the generator. a rotor of the screw expander is fixedly connected to a rotor of the generator; the power generation device drives the generator to generate power through rotation of the rotor of the screw expander; and a liquid refrigerant injection inlet and a refrigerant outlet are disposed on the generator cavity; the liquid refrigerant injection inlet is disposed on the top of the shell far from the expander cavity, the refrigerant outlet is disposed at the bottom of the shell near to the expander cavity; and the generator is cooled through evaporation of a liquid refrigerant, wherein the screw expander comprises a male rotor and a female rotor, and a shaft of the male rotor is fixedly connected to the rotor of the generator, characterized in that a first male rotor bearing is disposed at an end of the male rotor away from the rotor of the generator, and female rotor bearings are separately disposed at two ends of the female rotor, the male rotor comprises a rotor part and a connection part which are integrally designed, and the rotor part coordinates with the female rotor; the connection part extends into the generator; and the expander cavity and the generator cavity are isolated from each other through an isolation mechanism, so that a hole is formed between the expander cavity and the generator cavity; the connection part passes through the hole and enters the generator cavity, and an end of the connection part away from the rotor part is fixedly connected to the rotor of the generator.