A parallel hydrostatic power transmission is studied and the fluid division in the hydrostatic drive line is analyzed. The dynamic model of the machine is studied in two sections: a simplified model and an elaborated model. In both of the models all the acting forces and their effect on the vehicle's motion are studied and the dynamic behavior of the machine is calculated using mathematical equations. The speed of the machine cannot be controlled by a simple feedback control. It is concluded that a simple feedback controller does not provide the best performance for this application. The gain-scheduled PID controller is used for this application. This Type of controller can adapt itself with the variable dynamic characteristics of the hydraulic system. Gain scheduling is the major key in gain-scheduled PID controller. The results of tuning with different gains are shown and the Bode & step diagrams are presented. Several static tests on the machine have been done to monitor the behavior of the HST.