The intelligent automatic recognition method for infrared spectra of composite insulators is an important development direction for the maintenance and operation of composite insulators in the future. To obtain sufficient infrared spectrum samples of heating, insulators with five types of defects—sheath damage, skirt damage, conductive defects, semi-conductive defects, and floating conductive defects—were fabricated. The influence of contamination degree and humidity on the infrared test results was also analyzed. The results show that as the contamination degree increases, the temperature rise of the composite insulator increases accordingly. The highest temperature rise for insulators with sheath damage, skirt damage, and floating conductive defects is at the sheath of the high-voltage end, while the highest temperature for insulators with conductive and semi-conductive defects shifts to the top of the carbonized channel. Results also suggest that for different humidity levels, the temperature rise for various defects shows significant differences Under different defect conditions, the temperature rise increases with increasing humidity. Most defects show a moderate transition from 70% to 80% humidity, with a significant temperature rise change from 80% to 90% humidity.