Univ Sci & Technol China, Dept Modern Phys, Hefei 230026, Peoples R China
; CAS, Inst High Energy Phys, Beijing 100039, Peoples R China
BES II detector has been upgraded from 1995, the TOF time resolution is about 180ps for Bhabha events, a big improvement compared with 330ps of BES I. With the upgrade of the detector, the software including calibration, reconstruction and Monte Carlo (M. C.) simulation needs corresponding improvement, especially for M. C. simulation. Using 50M J/psi data taken in the last two years at BES II, we studied the TOF resolution carefully, and made some improvements for TOF MC simulation. After such an improvement, we compared the TOF resolutions between real data and M.C. data and found they agree with each other.