The determination and mathematical descriptions of the difference between the imaging radiation measurement and the non-imaging radiation measurement which is of maturity are necessary for extending the radiation measurement from non-imaging technology to imaging technology. In this paper, the mathematical descriptions of the imaging and non-imaging radiation measurement are deduced based on the basic equations of radiation measurement and the correspondence between the infinitesimal planes of the target and sensor array. Because the imaging plane does not change the radiation transfer between the target and sensor, the mathematical descriptions of the imaging effect can be obtained by comparing the two mathematical descriptions. A concrete analysis of the imaging effect based on pinhole imaging and lens imaging is carried out. The results show that the primary cause of the imaging effect is the imaging optical axis angle while the subsidiary cause is the imaging zenith angle, and the influence of the subsidiary cause is determined by the difference between the imaging optical axis angle and the imaging zenith angle.