  For the China Spallation Neutron Source (CSNS), a combination of the H-
stripping and phase space painting method is used to accumulate a high
intensity beam in the Rapid Cycling Synchrotron (RCS). In this paper, firstly,
the injection processes with different painting ranges and different painting
methods were studied. With the codes ORBIT and MATLAB, the particle
distribution and painting image were obtained. Then, the reasonable painting
range which is suitable for the aperture size and magnet gap can be selected.
Since the real field uniformity of BH3 and BV3 is not completely in conformity
with the design requirement, the painting method and painting range also need
to be selected to reduce the effects of bad field uniformity.
