This invention provides a thermal imaging device and a thermal image photographing method. In the prior art, when the thermal imaging device is used, a photographing part, photographing angle, and photographing distance of a photographed object are selected according to subjective experience of users, thus lowering photographing speeds and having omissions, and a position, dimension, and angle of thermal images of similar photographed objects in infrared thermal images photographed each time are different, causing subsequent analysis trouble. In this invention, via a reference image with a specified position and specified dimension presented in the infrared thermal image and reflecting specified morphological characters of the photographed object, a visual reference of predetermined thermal image quality and photographing requirements of the photographing object is provided, assisting the users to correctly grasp imaging states and photographing distances of the thermal image, thereby acquiring uniform normative thermal image of the photographed object.