Infrared thermal imaging technology has a wide application prospect in the field of building engineering. The influence factors in wall hollow defect detection by infrared thermal imaging are summed up and analyzed by using a H2640 type infrared thermal imager and the NS9200 Report Generator software. The influence of weather, shooting angle and image analysis software on the detection result are discussed and hence the best shooting time and angle are determined. Finally, the misjudgment factors and level\&span range calibration of the image analysis software are analyzed and the corresponding processing measures are proposed.