In allusion to the increasingly severe indoor formaldehyde pollution problem, a STM8S-based indoor formaldehyde detection system is invented. According to the system, a hardware anti-jamming circuit based on a subtracter is creatively designed. Thus, the problem of poor measurement accuracy caused by the adoption of temperature/humidity sensitive resistors for compensation of temperature and humidity coefficients of a sensor in previous formaldehyde electrochemical sensor detection design circuits is overcome; and acquired data undergoes soft optimization by combination of sampling filter algorithm and Lagrange's interpolation method. The system has formaldehyde concentration threshold setting and over-limit alarm functions as well as auxiliary functions such as temperature, humidity and perpetual calendar display, etc., thus truly realizing the combination of convenience and intelligence. Experimental results prove that the system has characteristics of high sensitivity and accuracy,simple operation, high cost performance and the like in practical application, and also can be promoted and applied in other occasions where formaldehyde concentration needs to be detected.