  The Rapid Cycling Synchrotron(RCS) of China Spallation Neutron Source(CSNS)
employs painting injection to achieve uniform beam distribution and suppress
space-charge effects. In the painting injection, the mismatch between the
injection beam orbit and circulating orbit could make the non-uniformity of
beam distribution and emittance growth, which may lead to beam loss. To match
the injection beam orbit and the circulating beam orbit, it is necessary to
identify the orbit of injection beam relative to the circulating orbit in the
injection point. However, it's hard to measure this relative injection orbit
directly. Theoretically, the relative injection beam orbit can be deduced by
measuring the turn-by-turn beam position of a single turn injection beam.
However, the intensity of single turn injected beam is too low to be measured
with sufficient signal-noise ratio by using beam position monitor(BPM). In this
paper, two effective methods based on multi-turn injection and turn-by-turn BPM
are given to perform the match between the injection and the circulating beam
orbit. The simulation results and application in the beam commissioning of
CSNS/RCS show the validity of the methods.
