A supercritical water oxidation treatment system for organic wastewater with a high salinity crystallizes high-salinity wastewater by a low temperature of liquid oxygen, and decreases an inorganic salt content in the wastewater. Under supercritical water conditions, a hydrocyclone (4) separates most precipitated solid salts in the wastewater, so effectively prevents pipes and the tubular reactor (22) after the hydrocyclone (4) from plugging. Inorganic salts are able to be continuously separated from the system by the hydrocyclone (4) at the bottom of a desalination device, In addition, excess oxygen and gaseous products CO2 are recovered by a separation recovery part. The reaction time and the reaction temperature of supercritical water oxidation reaction are lowered due to the installation of a simple post-treatment unit (37). Moreover, the heat of the reactor effluent with a high temperature is recovered in the system, so operation cost of the system is reduced evidently.