A new automatic measurement technique for 360 degrees surface topography of 3D diffuse objects is proposed in this paper. The technique bases on a new structured illumination method, called step projection, and a new algorithm. The principle, hardware and software of the automated measurement system are completely expressed. Some researchers are carried out on the accuracy of step projection. It is suitable for 360 degrees objects like asymmetrical cylinder, especially for objects with irregular surface. Besides this, it has many advantages, such as simple optical setting, lower cost, and easy determination of deformed line's position. Using the technique a 360 degrees 3D object with greater grads change on its surface can be reconstructed. The shape of flow passage of engine valve is very irregular. By using the automated rotation profilometry, it can be measured accurately. The experimental results are offered.