Numerical simulations based on the finite-difference time-domain technique are performed to investigate the transmission spectrum of defects in the two-dimensional (2D) rectangular lattice photonic crystal. The results show that the defect modes within the band gap are created by either decreasing or increasing the radius of normal GaAs rods and there exists a one-to-one correspondence between the two defects which possess different radius but similar resonance. In addition, the defect modes generated by decreasing size are single modes while those created by increasing size are doubly degenerate modes or multimodes. More importantly, the former defects are insensitive to the intensity of electric field while the latter ones exhibit strong dependence on the intensity of electric field. The conclusion might be used in the design of photonic crystal devices based on point defects.