We proposed a novel interference elimination method for CW-THz reflection imaging. Based on the study of interference mechanism in the imaging window, inverse processing was proposed to realize the interference elimination. Theoretical calculation showed that the interference phenomenon was closed related to the characteristics of imaging window. The refractive index and thickness of the window were the two main factors for the interference. Moreover, polarization was also taken into consideration for the CW-THz reflection imaging because the reflectivities of the s and p polarized waves were different from each other. This method was applied in different imaging systems for the demonstration of its feasibility. The high resistivity float-zone silicon (HRFZ-Si) plate was employed as the imaging window in the normal incidence system with a terahertz quantum cascade laser (THz-QCL) operating at 4.3THz. The oblique system employed quartz plate as the imaging window with an optical pumped THz laser operating at 2.52THz. Pork and liquid samples of water and edible oils were chosen as the imaging samples to demonstrate the interference elimination method.