Multispectral temperature measurement is an important method for measuring the surface temperature of the hot end of engines and heavy-duty gas turbines. However, due to the unfavorable factors such as large temperature difference in the background environment, uncertain humidity and electromagnetic interference, the weak signal processing of the multispectral surface thermometer is very difficult. This article focuses on the design of weak signal conditioning circuits for multispectral surface thermometers in complex environments. The near infrared detector which is suitable for multispectral surface thermometer is studied and selected. The accuracy of signal amplification is improved because of the technologies of guard ring and kelvin switch. The selection method of circuit board sheet, the circuit three anti-technology and the specific implementation of anti-electromagnetic interference are introduced. The experiment results show that the multispectral surface thermometer meets the measurement needs and has certain environmental adaptability.