Abstract: A new exploring method is presented for a robot carrying ultrasonic sensors to work in unknown environment. With a structural model developed for the exploring system and its operating principle described, an experimental investigation was done on some different surfaces which form basically an unknown and unstructured environment, such as plane, circular, inclined and vertical surfaces. The experimental results showed that the ultrasonic rangefinder doesn't fit to explore the circular surface of small radius of curvature. As for the other three surfaces, different ways were proposed for exploration and data processing separately as a result of the experimental study, i.e., three ultrasonic sensors arc necessary for inclined surface; the dynamically measuring errors resulting from patulous angle should be compensated for vertical surface; moving sensors should be compensated for plane surface.