  The correction of closed orbit has great influence on the operation of
synchrotron. The design of correction system is one significant component of
lattice design. It is suggested to set BPMs at the peaks of betatron
oscillation. The correctors need to be located at the positions where \b{eta}
function is large or the sources of large errors. In the simulation of the
closed orbit correction of HIMM synchrotron, one important reason affecting the
result of horizontal correction is the longitudinal alignment error of dipole
magnet. It is advisable to decrease this kind of alignment error while the
deflection angle of dipole magnet is large.
