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Thomson scattering is one of the most important diagnostic methods for measuring plasma electron temperature (T e) and electron density (n e). In the diagnostic system, the polychromator is often used to analyze the spectral broadening and intensity of the detected scattered light. The performance of the avalanche photodiode (APD) used in the polychromator is greatly affected by the ambient temperature. The change of ambient temperature will seriously affect the accuracy of Thomson scattering diagnosis. Through experimental analysis, when the ambient temperature increases, the gain of APD will be significantly reduced, resulting in a significant deviation in electron density measurement. Taking the system response at an ambient temperature of 24.1 °C as reference, the deviation of electron density measurement varies from 43% to −16%, with the ambient temperature from 16.6 °C to 29.9 °C. However, the change of ambient temperature has little impact on the measurement of electron temperature. Detailed test of the polychromator shows that the estimated deviation of the electron temperature is within 3%. Due to the change of ambient temperature, the response of the detectors in each channel of the polychromator is inconsistent, which will cause random errors. The influence on electronic temperature calculation is analyzed by numerical simulation. [ABSTRACT FROM AUTHOR]