The band gap for 2D PhC with different modes and different lattice structures using FDTD has been computed. Three PBGs between the first and the second bands, between the second and the third bands and between the fourth and fifth bands are concluded. Simulation results shows that for band structure computation is of 1D PhC using FDTD, it is found that some additional solutions appear, which are drop out from the general set. They are called spurious solutions. Such solutions appear due to space discretization and because of finite solution time interval and these could be eliminated manually.