This study is about the cooling system of the hybrid bus using the hydraulic fan drive system for the package design and the fuel consumption. It is developed the cooling module combined the engine cooling and hybrid system cooling, and optimize the package design using the CFD tools. The fan control logic is made with the ambient temperature, each fluid temperature, water pump speed, etc. for the balance between the fuel economy and the cooling performance. In addition, the safety of the hybrid system is improved through the cooperation control with the host controller. As a result, the cooling system package volume is reduced 30% in comparison to the concept design, and the fuel consumption is improved 4%.