Infrared thermal imaging technology is a new nondestructive detection technology, which is widely used in pressure vessel detection. In this paper, three-dimensional temperature distribution model of pressure vessel with defects is established, and the influence factors on infrared detection of pressure vessel defect are researched. The influence of environmental factors, thermal excitation strength, thermal excitation time and defect size on infrared detection is analyzed. The results show that: (1) increasing thermal excitation can degrade the maximum reduced temperature when infrared radiation thermal excitation temperature is lower than 200°C, while the reduced temperature can be raised with the increased thermal excitation when the temperature is higher than 200°C. (2) the maximum comparison temperature increased first and decreased afterwards with the increasing thermal excitation time, finally reduce to the comparison temperature under steady state. (3) the influence of wind speed and surface blackness in environmental factors on infrared detection precision is greater.