Millimeter wave (MMW) images are widely used for the detection of contraband in human security screening. However, at this stage different pre-processing (PP) methods have a significant impact on the accuracy of MMW image target detection. To address this issue, we pre-processed the data by spatial filtering, spatial filtering plus maximum clustering and spatial filtering plus minimum clustering, and compared the accuracy of target detection by different methods. The experimental results show that all three methods can effectively improve the target detection accuracy, with spatial filtering being the best pre-processing method, achieving an accuracy of 92.3%, which is an improvement of about 4% compared to the original data without PP. It indicates that the spatial location-based filtering method is more effective than the reflection intensity-based clustering filtering method in improving the accuracy of MMW image detection, which can be used to improve the accuracy of the active MMW hologram. The task of improving the accuracy of active MMW hologram target detection provides a reference point.