Abstract: The Rapid Cycling Synchrotron (RCS) of the China Spallation Neutron Source (CSNS) is a high intensity proton accelerator. The study on the coupling impedance in the ring plays an important role in the stability of the beams. The total impedances of the ring and the occurrence of the beam instability can be controlled by evaluating of the coupling impedance accurately. The impedances of some main components in the RCS ring, such as RF cavities and collimator were calculated by using numerical simulation. The impact of bus-bar’s configuration on RF cavities and beams was estimated by impedance calculation. To solve resonance thoroughly, the inherent frequency should be more than 10 MHz by designing bus-bar’s structure again. Furthermore, the RF shield of primary collimator was introduced, which shows a significant reduction of both the longitudinal coupling impedances and the loss power with small installation cost.