The mode properties of symmetric and non-symmetric one-dimensional photonic crystals with a sandwich layer defect were investigated by using the optical transmission matrix method.Results show that many defect modes may exist for one defect;the defect modes disappear in the non-symmetric structure but still exist in the symmetric structure as the sandwich layer vanishes.Comparison shows that both the position and the number of the defect modes move linearly towards the long wavelength region with the increase of the optical length of the sandwich layer in both cases,while the speed of the motion of the defect modes with the optical length of the sandwich layer is approximately the same and inversely proportional to the order of the defect mode in both cases.