In this paper, co-phasing errors of a segmented primary mirror tiled by hexagonal segments are successfully calculated for the 12-meter Large aperture Optical/infrared Telescope（LOT）. Co-phasing errors including out-of-plane errors are simulated separately and comprehensively based on several software simulation platforms. PAOLA simulation results show that the Strehl Ratio（SR） of LOT is larger than 0.8 when the RMS value of tip-tilt obeying a normal distribution is less than 0.018 arcsec, and the SR of LOT is larger than 0.8 when the RMS value of piston obeying a normal distribution is less than 40 nm. Besides,simulation results of Zemax show that the SR of LOT is larger than 0.8 when the RMS value of tip-tilt obeying a normal distribution is less than 0.02 arcsec, and the SR of LOT is larger than 0.8 when the RMS value of piston obeying a normal distribution is less than 40 nm. These simulation results successfully lay a solid foundation for LOT（especially the segmented primary mirror with active optics）