The linear internal combustion engine-linear generator integrated system (LICELGIS) is an innovative structure as a range-extender for the hybrid vehicles, which contains two opposed free piston engines and one linear generator between them. The LICELGIS is a promising power package due to its high power density and multi-fuel flexibility.In the combustion process of linear engines, the top dead center (TDC) position is not stable in different cycles, which significantly affects system operations. Otherwise, pistons move away from the TDC with high-speed because of the tremendous explosive force, which incurs the short residence time of pistons around the TDC and rapid decrease of in-cylinder temperature, pressure and the combustion efficiency. In order to address this problem, a scientific simulation model which includes dynamic and thermodynamic models, is established and a combustion optimization control strategy is proposed. The control strategy is based on the variable electromagnetic resistance force of the system. The electromagnetic resistance force is predictive and adjustable based on the velocity of midpoint and piston displacement.The simulation results indicate that under this control strategy, the TDC position is stable in different cycles and the power of the linear engine in one working cycle increased 5.6% than that without this control strategy. The control strategy based on combustion law and compression ratio of different fuels should be useful to control the piston trajectory around the TDC or even the whole cycle to realize high-efficiency combustion of different fuels.