At present, the torque characteristic of hydro turbine is extended and fitted by the experience and mathematical methods in transient process calculation of hydropower station. The calculation results are inconsistent with the testing results. In this article, the treatment of hydro turbine torque characteristic curve was studied based on load shedding test. The torque characteristic curve of the zero-opening was identified by the shedding test data. The whole torque characteristic curve was extended and fitted by the least square method. The torque characteristic curve obtained by this method was used to simulate the load rejection transition process, and the calculated results were compared with the test results. The calculation results of the extreme value and adjustment process are consistent with the test results, this torque characteristic curve can be used to accurately simulate the regulation process of the hydro turbine governor. The simulation accuracy of the transient process is greatly improved. The research of this article can effectively guide the safe operation of hydroelectric unit.