Hardware In the Loop Simulator (HILS) method was declared in march 2007 as fuel consumption and exhaust emission test of hybrid electric heavy duty vehicles. Accelerating and breaking of HEV model with vehicle parameters is simulated by driver model of HILS system. And then JE05 driving test mode is virtually run on the HILS system. In this study, sensitivity analysis of inputting parameter to HILS parallel-HEV model was conducted in order to assess the effect of vehicle parameters on fuel consumption simulated by HILS system.