To study the forming quality during ring pipe hot push-expanding, the hot push-expanding experiments of β titanium alloy were carried out, and the process of hot push-expanding was analyzed by a mesh method and a finite element method. Moreover, the causes of quality defects, such as corrugate, cracking, wall unevenness, and ellipticity, were discussed. The results show that ram-horn mandrel, expanding radio, temperature and velocity are important parameters which influence the forming quality of ring pipe. They interact with each other and need a coordinated control. The coordinated control principle is that the ram-horn mandrel and the expanding ratio should be set, the temperature is a key factor, and the velocity is a coordination factor.