The prestressed concrete cylinder pipe(PCCP) has been widely used in underground water conveyance projects, especially in the south-to-north water diversion project. Pipeline interface belongs to the semi-rigid structure; while the relative angle of adjacent PCCP is larger than the allowable angle, PCCP will produces internal force in bell and spigot. However, if it is located in the serious uneven soft soil foundation, it may produce excessive angle and even destroyed. Therefore, how to control the PCCP produce excessive angle in soft soil foundation becomes one of the key issues in researching pipeline safety. Firstly, what factors lead to relative angle is analyzed. Then combined with field test and numerical analysis, the key factors for control PCCP angle is determined. Research results show that the thickness of the gravel cushion, the thickness and compactness of the sand cushion are the most important factors to control excessive angle. As the thickness of the gravel cushion, the thickness and compactness of the sand cushion increase, the relative angles decrease. The research results can provide basis and guidance for PCCP pipeline engineering design in soft soil foundations.