To increasing the efficiency research a single cylinder linear engine with spring system has been done. Issues raised in the study was the analysis of air flow into the combustion chamber in a single cylinder linear engine, with a spring system for its return cycle. Solidworks has been used to design and simulation as well. This study compared the fluid flow in the combustion chamber between the conventional engine and linear combustion engine. The parameters used are the engine speeds 1000 rpm, 4000 rpm and 4500 rpm. The speeds is chosen because has been predicted that the inlet port on the linear engine can not work properly. Results of analysis that has been done appears average pressure of conventional has a higher value than the linear combustion engine. The same thing happened in velocity, in the average value of the conventional engine is higher than the linear combustion engine.