The modulation of optical thickness on transmission spectrum of one-dimensional photonic crystal was studied by using transfer matrix theory.The results show that the transmittance,frequency and bandwidth of transmission peak are not changed with increasing the optical thickness of medium when the optical thickness of A and B medium are equivalent (DA=DB);when the optical thickness DA and DB are not equivalent (DA≠DB),with increasing DA or DB or DA and DB,the transmittance of transmission peak is not changed,but the bandwidth is widen,and when DA>DB,the transmission peak shifts to higher frequency,on the contrary,the transmission peak shifts to the lower frequency.These laws of modulation can provide a useful reference for construction of the photon crystal model and design of narrow band optical filter and optical switch.