The invention discloses a vertical single-cylinder methane engine gas inlet and combustion system comprising a gas inlet system and a piston combustion chamber. The gas inlet system comprises an air filter, a mixer assembly, a filter assembly, and a throttle valve. The air filtered by the air filter and the methane filtered by the filter assembly are discharged into the piston combustion chamber after being mixed inside the mixer. The throttle valve is installed on the mixer assembly and is used for controlling a mixed gas output. Actions of the throttle valve are controlled by an auxiliary electronic control system. Being an engine using the methane as an energy source gas on a vertical single-cylinder model, the vertical single-cylinder methane engine has the advantages of small size, low cost and convenient movement. Additionally, the fuel gas can be controlled in real time to be matched with the working condition based on instructions by replacing the original mechanical device with the auxiliary electronic control system, thereby reasonably matching the fuel gas with the working condition of the engine, and improving the combustion property greatly.