A liquid pump of a screw expander, applied to an Organic Rankin Cycle, comprising a semi-sealed or fully sealed shell, wherein an expander male rotor, an expander female rotor, a liquid pump male rotor and a liquid pump female rotor are disposed in the shell; an end of the expander male rotor is fixedly connected to the liquid pump male rotor, and the liquid pump male rotor rotates under driving of the expander male rotor; the shell comprises an expander cavity and a liquid pump cavity isolated from each other; all or a main body part of the expander male rotor, and the expander female rotor are disposed in the expander cavity; all or a main body part of the liquid pump male rotor, and the liquid pump female rotor are disposed in the liquid pump cavity; an expander suction inlet, an expander exhaust outlet, a liquid pump inlet and a liquid pump outlet are disposed on the shell; the expander suction inlet and the expander exhaust outlet are respectively connected to an outlet of an evaporator and an inlet of a condenser; the liquid pump inlet and the liquid pump outlet are respectively connected to an outlet of the condenser and an inlet of the evaporator; the expander male rotor comprises a first rotor part and a first connection part which are integrally designed; the first connection part is for connecting the first rotor part and the liquid pump male rotor in the liquid pump cavity, the first rotor part is disposed in the expander cavity and coordinates with the expander female rotor; and the first connection part extends into the liquid pump male rotor in the liquid pump cavity; the liquid pump male rotor comprises a second rotor part; the second rotor part is disposed in the liquid pump cavity and coordinates with the liquid pump female rotor; expander female rotor bearings (4061, 4062) are separately disposed at two ends of the expander female rotor, and liquid pump female rotor bearings (4071, 4072) are separately disposed at two ends of the liquid pump female rotor; a first male rotor bearing is disposed at an end of the expander male rotor away from the liquid pump male rotor; a second male rotor bearing is disposed at the first connection part and between the first rotor part of the expander and the second rotor part of the liquid pump; and the expander cavity and the liquid pump cavity are isolated from each other through an isolation mechanism, so that a hole is formed between the expander cavity and the liquid pump cavity, and the first connection part passes through the hole and enters the liquid pump cavity. the shell comprises an expander cavity and a liquid pump cavity isolated from each other; all or a main body part of the expander male rotor, and the expander female rotor are disposed in the expander cavity; all or a main body part of the liquid pump male rotor, and the liquid pump female rotor are disposed in the liquid pump cavity; an expander suction inlet, an expander exhaust outlet, a liquid pump inlet and a liquid pump outlet are disposed on the shell; the expander suction inlet and the expander exhaust outlet are respectively connected to an outlet of an evaporator and an inlet of a condenser; the liquid pump inlet and the liquid pump outlet are respectively connected to an outlet of the condenser and an inlet of the evaporator; the expander male rotor comprises a first rotor part and a first connection part which are integrally designed; the first connection part is for connecting the first rotor part and the liquid pump male rotor in the liquid pump cavity, the first rotor part is disposed in the expander cavity and coordinates with the expander female rotor; and the first connection part extends into the liquid pump male rotor in the liquid pump cavity; the liquid pump male rotor comprises a second rotor part; the second rotor part is disposed in the liquid pump cavity and coordinates with the liquid pump female rotor; expander female rotor bearings (4061, 4062) are separately disposed at two ends of the expander female rotor, and liquid pump female rotor bearings (4071, 4072) are separately disposed at two ends of the liquid pump female rotor; a first male rotor bearing is disposed at an end of the expander male rotor away from the liquid pump male rotor; a second male rotor bearing is disposed at the first connection part and between the first rotor part of the expander and the second rotor part of the liquid pump; and the expander cavity and the liquid pump cavity are isolated from each other through an isolation mechanism, so that a hole is formed between the expander cavity and the liquid pump cavity, and the first connection part passes through the hole and enters the liquid pump cavity.