Mixed unsaturated fatty acid which mainly contains C₁₈ were hydrogenated with the Ni unitary as the catalyst under different temperature.The focus is laid on the trend of the iodine value and freezing point which change with the service temperature at various points of time or pressures. Then the adopted service pressure and time were found to be 0.4MPa and 1.0h. And the tropic and formula of iodine value-temperature and freezing point-temperature were obtained. The best service temperature was calculated to be 190℃.