There is provided a high efficiency ocean thermal difference power generating system by using liquid-vapor ejector and motive pump comprising: an evaporator for changing transferred refrigerant liquid into refrigerant vapor with high temperature and high pressure by the thermal exchange with surface seawater; a vapor-liquid divider which is installed at the outlet part of the evaporator and divides the refrigerants to liquid-state refrigerant and vapor-state refrigerant respectively; a distributor which is installed at the inlet of the evaporator and distributes the refrigerants flowed into the evaporator to multi-paths; a turbine for generating electric power by using the high pressure refrigerant vapor transferred from the liquid-vapor divider or the evaporator; a motive pump for increasing the pressure of the refrigerant liquid distributed from the distributor or the liquid-vapor divider; a liquid-vapor ejector for mixing the low pressure refrigerant vapor which passed the turbine and the high pressure refrigerant liquid which passed a motive pump, thereby proceeding expansion and compression; a condenser for condensing the refrigerants which was mixed in the liquid-vapor ejector by the thermal exchange with deep seawater; and a refrigerant circulation pump for increasing the pressure of the refrigerants which was condensed in the condenser up to the evaporation pressure and for circulating.