Abstract: In order to propose a novel method to measure the mass fraction of fructose, plane wave expansion method for photonic crystal was adopted. A 2-D photonic crystal with a square lattice and triangle lattice of circular cylinders was designed in the Si background semiconductor material. The TE mode and TM mode band gap structure characteristics of square lattice and triangular lattice air hole structure photonic crystal were achieved.The results show that for isotropic photonic crystal of either square or triangular array arrangement, it is easier for the dielectric air type photonic crystal to form TE-polarized mode band gap in high-frequency region. Lattice structure has a certain impact on photonic band gap, TE mode band gap is much larger than the TM mode in both square and triangular structure photonic crystal. The photonic band gap changes with the difference of the mass fraction of the fructose solutions, which are used as the dielectric material in the air hole.