As part of a study involving methods of control of an axial piston pump, it is required to obtain linear or linearized equations of motion of the system’s states. The torque imposed on the plate by the pumping action of the pistons is the most important term in the equation of motion of the swashplate. The torque is a result of a nonlinear and partly discontinuous relationship; this relationship being a function of the geometrical features of the pump and the system operating conditions. Mathematical equations describing swashplate torque are derived from general hydraulic and mechanical considerations given in this paper. This mathematical model can be linearized so that linear parameters for the equation of motion of the swashplate can be obtained. In addition, results of predictions made by the model are presented and compared with some experimental data provided by Sundstrand. An indication is also given as to changes in torque resulting from variation in swashplate angular velocity and timing position of the valve plate.