Abstract: Focusing on the obstacle-detection in the robot working space, this paper presents a new detection method which is different from the conventional ultrasonic range measurement, makes research on the theory about ultrasonic range-measurement of extremely short-range obstacle in sphere space and avoid cross talk by using the correlation algorithm, improving ultrasonic range measurement precision.It uses a specially-distributed ultrasonic sensor array for ultrasonic range measurement and the locating algorithm with three points on a sphere can detect not only the space distance of the obstacle, but also the space orientation of the obstacle.