Abstract: In this article, a control model composed of a turbine governor, penstock, pump-turbine, and generator, is developed to study the influence of pump-turbine characteristics on system stability. Classical control theory was applied to derive expressions for the synthetic coefficients. Based on the real pump-turbine characteristics of 19 sets collected from model tests, polynomial surfaces were fitted for the relationships of unit flow and unit torque versus unit speed and guide-vane opening. Combining these relationships with the expressions of synthetic coefficients, we can reveal the trends of variations in the six transfer coefficients and the synthetic coefficient and thus obtain the influence of pump-turbine characteristics on system stability at different water heads. Finally, numerical simulations of several working conditions were conducted, which validates our conclusions.