By using the plane-wave expansion method and fast-Fourier transform method, two dimensional photonic band structure is calculated. A two-dimensional triangular lattice photonic crystal (Si and Ge) is used as the substrate, and the air hole is filled with different molality of mixed binary solution materials under test. The photonic band gap of the photonic crystal filled with binary solution under different polarization modes is obtained. Simulation experiments show that the molality of solution has a linear relationship with photonic band gap width, and that the linear correlation degree is affected by background medium column material. When the binary solution is used as the dielectric material of the air hole, the photonic band gap (PBG) changes with different molality of the solution quality. This research has a certain guiding function in solution mass fraction detection applications.