As the application field of security robots are expanded, the complexity of their working environment increases. In special environments such as smoke, dust and dark, the navigation system with visual and laser navigation manners are no longer applicable. Aiming at this problem, based on the research on the principle of the distance measurement with millimeter-wave radar, firstly, the research of two pulse canceller is carried out to filter out the static clutter. Then, a dynamic threshold detector is designed to accurately obtain the distance between the millimeter-wave radar and mobile robot. In order to improve the navigation accuracy, a segmentation clustering method is proposed to process the distance data set. Finally, a security robot navigation system based on the principle of triangulation was designed. Experiment results show that using the segmentation clustering method, the robot navigation accuracy is higher compared with that using the mean method. The robot can operate along the set straight and curvilinear lines in smoke and dark environment. The navigation error is about 0. 11 m.