Starting the first cycle of the first cycle of combustion in the idle start-stop technology is the key link. For the first cycle of the compression stroke, the self-ignition and misfire of the air-fuel mixture in the cylinder are easily caused. The FIRE software is used to establish the first-cycle first-cylinder oil and gas hybrid simulation calculation model. When the piston is at the position 60 before top dead center, different injection quantities, different in-cylinder flow fields, oil and gas mixing fields, and temperature fields are simulated and calculated. The optimal relationship between the fuel injection quantity and injection timing of the normal combustion of the first cylinder is given.