The application of photonic crystal in the solution concentration detection is investigated by using plane wave expansion method. A two-dimensional triangular lattice photonic crystal (Si and Ge) is chosen as the substrate,filling the air hole with different percentage concentration of mixed binary solution materials which will be measured,and the photonic band gap of the photonic crystal filled with binary solution under different polarization modes is obtained. The results show that when the binary solution is used as the dielectric material in the air hole, the photonic band gap (PBG) changes with the different percentage concentrations of the solution quality. This has a certain guiding function in solution mass percentage concentration detection applications.