The invention provides a real-time mixed gas concentration monitoring system. The real-time mixed gas concentration monitoring system comprises at least two mass flow control modules, a mixing module,a pressurizing module, a detection module and a proportional control module, wherein the mass flow control modules output gases with different mass flows; the mixing module mixes the gases with different mass flows, which are output by the mass flow control modules; the pressurizing module pressurizes mixed gas; the detection module detects the concentration of the pressurized mixed gas; the proportional control module judges whether the concentration of the mixed gas meets the set concentration, and issues a control command to the mass flow control modules when the set concentration is not met. The real-time mixed gas concentration monitoring system can achieve real-time monitoring of the concentration of the mixed gas in the preparation process, so that the preparation accuracy of the mixed gas is improved and the environment pollution is avoided.