An optimization etching model of the traps surface is proposed for the multicrystalline silicon surfaces. Based on uncertainty principle, the dependence of the photon scattering direction on the size of salient point on the internal surface of trap-pit is studied. The relationship between the topography of pit and the reflectivity is deduced using Fourier transformation. The theoretical analysis results indicate that the U-trap with the internal surface full of salient points has low reflectivity compared with V-trap with the internal surface full of salient points. However, the reflectivity of U-trap with the smooth internal surface is higher than that of the V-trap. The topography of multicrystalline silicon surface in different models textured with alkaline solution are observed by scanning electron microscope. It is found that \[100\], \[111\] and \[110\] planes is covered with canyon-structures, distorted U-trap and hybrid structures, respectively. The reflectances of different crystallographic planes are measured, showing that the U-trap′s reflectance is the smallest. And it proves the proposed model.