Abstract: In order to segment multiple brightness temperature targets in passive terahertz images and meet the requirements of terahertz inspection security systems for extracting different brightness temperature targets, a passive terahertz image segmentation method based on multiphase level sets is proposed. The traditional method of using a single level set function can only divide the image into two regions. When there are multiple brightness temperature target objects in the image, they can not be completely extracted. The proposed method uses multiple level set functions for evolution, which can segment the image into multiple regions and meet the needs of segmenting multiple bright and warm objects. Using the multiphase level set method to process multiple target objects, experimental results show that this method can extract multiple bright temperature target objects hidden under human clothing in passive terahertz images. Compared with the single level set method, it improves the accuracy of the extaction.