The invention discloses an ocean heat energy open circulation power generation system which comprises a flash evaporator, a warm seawater pipe, a warm seawater pump, a low-pressure steam pipe, a front-arranged small steam turbine, a steam compressor, a high-pressure steam pipe, a main steam turbine, a power generator, a steam exhaust pipe, a surface type condenser, a cold seawater pipe, a cold seawater pump, a steam pumping pipe and a heat exchange pipe bundle. Low-pressure steam is divided into two channels, one channel of low-pressure steam enters the front-arranged small steam turbine to do work to drive the steam compressor to work, the other channel of low-pressure steam is compressed by the steam compressor to become high-temperature high-pressure steam, the high-temperature high-pressure steam then enters the main steam turbine to do work to drive the power generator to generate power, part of steam is pumped from the main steam turbine to be used for heating seawater in the flash evaporator, and the amount of the steam generated by the flash evaporator is increased. According to the ocean heat energy open circulation power generation system, the size of the steam turbine in existing open circulation is effectively reduced, and the problem that the unit capacity is limited is solved; the ocean heat energy open circulation power generation system has the advantages of being high in system heat efficiency, high in water power utilizing rate, high in net power generated power and the like.