The main objective of designing the powertrain mount system is to decrease the vibration transmission from the powertrain to the body. The powertrain mount system has enormous effect on the ride comfort of the automobile. The reasonable design of powertrain mount system could not only decrease greatly vibration and noise produced by engine, but also could lengthen the life of the parts. Therefore, it is very important that design of powertrain mount system.The purpose of this paper is to develop an analytical optimum software to assist the design engineer in arriving at a mounting configuration with the most potential to achieve all the desired performance goods without violating size of the engine compartment. 6 DOF (Degree of Freedom) nonlinear mechanical model of powertrain hydraulic mount system is set up. The hydraulic mount''s position, orientation, stiffness and damping are considered as the optimum variables. The optimum objective functions are 1) uncoupling of energy; 2) rational disposition of intrinsic frequency; 3) minimum of reflect force at mount''s position. The methods used in optimum are Flexible Tolerance Method and Generalized Reduced Gradient Method. The comparable figures and charts between before and after optimization will be given as results of this study. Based on this optimum design and associated papers, the software named ODPHMS (Optimum Design of Powertrain Hydraulic Mount System) is developed.The software is designed under OOP (Object Oriented Program) theory and it has been successfully applied for the design and reconstruction of the powertrain mount system of national car.