For China Spallation Neutron Source (CSNS), the septum magnets are the key part of the injection system and the lambertson magnet is the key part of the extraction system. If the leakage fields of the septum and lambertson magnets are large enough, the circular beam orbit of Rapid Cycling Synchrotron (RCS) would be affected. In this paper, during the beam commissioning, the leakage fields of the septum and lambertson magnets will be studied and their effects on the circular beam orbit will be given and discussed.
Proceedings of the 61\textsuperscript{st} ICFA ABDW on High-Intensity and High-Brightness Hadron Beams, HB2018, Daejeon, Korea