The relations of band gap widths of four photonic crystal structures (square lattices of cylinder medium, triangle lattices of square medium, square lattices of square medium and triangle lattices of square medium) and the size of medium are studied by the plane wave expansion method. Then the plane wave expansion method is used to calculate the modes of normal lattices and surface defect lattices, and composite the results. The results show that the band gap width of the same photonic crystal lattice increases at first and then decreases. The maximum of band gap width is obtained. The surface mode curves of the four lattices are all declining as the size of surface medium column increase. The square lattices, comparing with the triangle lattices, could have a larger range to change the size of the surface medium column, but get a smaller surface mode range.