Currently, almost all automotive and supplier companies are trying to expand model based development (MBD) for control system development. To shorten the development period, concurrent development of hardware and software is effective. Moreover, the control logic complexity is becoming higher in accordance with the implementation of new sensors, actuators, improved control system performance, and increased the interface with another ECU. One significant process of the MBD is the ECU verification with the plant model installed in HILS. We describe some key points for HILS in hybrid system development.