In this paper, a multi-component toxic gas monitoring system based on STM32 microcomputer and µCOS-II embedded operating system was built for the safety of field workers in contaminated sites. The system can monitor the concentration of toxic gas such as hydrogen cyanide, hydrogen sulfide, carbon monoxide and sulfur dioxide in real time on the contaminated site under restoration and display it on HMI. When concentration of toxic gas exceeds the threshold limit, the sound-light alarm will be triggered to warn related personnel to evacuate in time.