An experimental paltform for simulating the starting process of a PFI engine was set up. The contrastive analysis of prototype engine between conventional start with starting motor and high-speed cranking start with ISG (Integrate Starter/Generator) was carried out. Variation regulation of the transient engine speed, the cylinder pressure, the fuel compensation factor, the intake manifold pressure and the transient HC emission were elaborated. The results show that, with the increase of cranking speed, the intake air pressure dropped, and the intake air quantity reduced as well. The duration of fuel evaporation was shortened, so the fuel atomization was insufficient. The possibility of misfire was increased and the transient HC emission was prominent. All these phenomena had a close relationship with ECT (Engine Coolant Temperature). Fuel compensation in the first few working cycles during starting process could make the original lean mixture more preferable in order to improve the combustion environment.