Abstract: Based on the linear engine prototype designed independently, the starting experiment of linear engine was carried out. The calculation formula of the cycle intake air of linear engine in low revolution was obtained by using the speed-density method and the injector flow characteristic was calibrated through experiments. With this formula and the flow characteristics of injector in linear engine, as well as intake pressure and cylinder pressure data, it was calculated that the air fuel ratio was 7.92 and the total heat release was 66 J at the engine speed of 575 r/min when the fuel injection pulse width was 5.4 ms and the ignition timing was 1.0 mm before the top dead center. The results showed that, when the piston was at 26 mm before the top dead center, the linearity between the cycle intake air quality and the intake air pressure in intake port reached the best value of 0.03. The results can provide reference materials to the analyses of air fuel ratio and combustion characteristics of linear engine.