When the Millimeter-wave (MMW) radiometric imaging is carried out indoors, the radiometric temperature contrast between the target and the background decreases sharply, which leads to degradation of MMW radiometric images and difficulty in recognizing targets. Based on the realistic problem of MMW radiometric imaging for detecting contraband concealed on personnel indoors, the radiometric temperature transfer model was put forward. At the same time, both the apparent temperature distribution and radiometric temperature contrast between target and human body were deduced. Combined with the specific parameters of some typical targets, the reason for low indoor radiometric temperature contrast was analyzed. Then, the method of noise illumination was adopted in the application of indoor radiometric imaging, and the contribution of this method to the improvement of indoor radiometric temperature contrast was emphatically investigated. Moreover, from the perspective of radiation power density, it was proved that noise illumination was safe to human body. Both the theory analysis and simulation results are presented to demonstrate the feasibility and significance of noise illumination.