Spacecrafts in orbit are being threatened by space debris, so many countries have developed detection technique for space debris, and the diffuse reflection laser ranging of space debris is a new technology. According to the characteristic, the development and the status in the world of space debris diffuse reflection laser ranging, we research the diffuse reflection laser ranging system at Yunnan Observatory. The probability of detecting space debris by diffuse reflection laser ranging at Yunnan Observatory and the structure of systems and the key techniques for diffuse reflection laser ranging are analyzed. The feasibility of space debris diffuse reflection laser ranging at Yunnan Observatory is confirmed by experimentation method. Measurement data indicate that the precision of diffuse reflection laser ranging is 50～250 cm.