The computational scheme consists of two parts: 1) The nitrogen concentration in the inlet charge is constant, the intake oxygen is replaced by water at a temperature of 298K to simulate the comprehensive effect of dilution, thermal and chemical effects of IMWI, and the intake temperature reduces with water injection. 2) The oxygen concentration is equal to that of the previous part, the intake oxygen is replaced by nitrogen to simulate the dilution effect of IMWI, and the intake temperature is constant at 333K. With the comparison of the above results, the thermal and chemical effects of IMWI are obtained.