Abstract: Viscosity damping coefficient is an important dynamic parameter of diesel engine. In this paper the test and identification theory of viscosity damping coefficient were introduced from the linear and nonlinear model of governor. From the linear model the calculating formula and process for the damping coefficient were derived. The method and step to identify damping coefficient by simulating calculation of nonlinear model were developed. Combining the test result and the practical conditions of the linear and nonlinear model identification, some testing conclusions concerning the viscosity damping coefficient of governor were described.