In order to allow people to explore potential fire environments without risk of danger, a new fire scout mobile robot used in urban environments is introduced in this paper. It adapts itself to stair climbing by using articulated-chain-wheeled mobile style with differential wheels. The positive pressure with continuous flow of protected gas inside the body endows the robot with explosion protection capability. When the wireless control signal is interrupted, it could automatically return to safe place along previous path based on sensorial data. Since position estimation only using encoders reading has serious limitations as mobile robot movement proceeds, a novel method integrating data of encoders and ultrasonic sensors is built, which uses iterative closest point algorithm to do data matching so as to adjust position and orientation of the mobile robot. This path retracing method realizes high accuracy and fast speed of automatic returning when the mobile robot is working in static urban environment even if the environment is unknown.