In the community of green energy utilization, it has been a key issue to effectively enhance the light conversion of thin film silicon solar cells. A rear surface reflector structure of thin film silicon solar cells based on triangular one-dimensional diffraction gratings is designed, which can effectively enhance the light utilization efficiency of the solar cells. With a variety of grating structure types, inclination angles, grating periods and grating separations, the light reflectance of the rear surface of thin film silicon solar cells are respectively studied via the finite difference time domain (FDTD) method. The results indicate that the one-dimensional grating structure consist of isosceles right triangles gives rise to an optimal rear surface reflectance, and the reasonable increase of the grating period can also enhance the light reflectance of rear surface of the silicon solar cells. Besides, the study in this work also shows that there appears a resonance peak in the reflectance curve when the light wavelength matches the grating period of the gratings. Based on this diffraction characteristics, the one-dimensional grating structures proposed in this work can also be utilized as a wavelength selector in future designs.