Dynamic behaviors of the Hydro-Static Transmission (HST) systems are studied expermintally and theoritically. A linearised mathematical model of HST system is formulated. Parametric sensitivity using state variable analysis has been shown that there are two dominanat poles. The damping ratios associated with these polesare reduced by a noticeable percent when bulks modulus and volumatric displacement of the hydraulic motor are changed by ± 20 % of its nominal value, while an increase in leakage can lead to unstable system. A computer controlled test rig is developed and the response of the system states are measured. Experimental response of the system states are compared with the simulated results. The performance is improved after introducing Linear Quadratic Regulator (LQR) controller. The work outlined in this research represents a step in the optimal design process of hydrostatic transmission system.