The controlling technology of micro-structure on the surface of monocrystal silicon is a hot spot issue in semiconductor and solar cell fields because the conversion efficiency of monocrystal solar cell is affected by the structure of pyramid. With the traditional alkaline solution, monocrystal Si surface is easily textured, and becomes the surface full of the pyramid. However, it is difficult to control the sizes, the shapes and the distribution of pyramids in the process. In this paper, we discuss how a new additive influences the sizes, and the shapes of pyramids during the etching process. In experiment, silicon is etched in traditional alkaline solution with addition of the new additive at a fixed temperature and time. Samples are scanned by SEM. The SEM result shows that the samples are uniformly-densely filled with pyramids with smooth edges. The size of pyramid is smaller than that etched in the traditional alkaline solution. The etched surface is covered by pyramids with 24m in size. The reflectance spectrum of the textured surface is measured. The measured reflectance decreases to 12.51%. These experimental results show that the new additive can effectively cantrol the sizes and the distribution of pyramids on the silicon surface during the texturing process, which is very meaningful to control the textured structures of single crystal silicon surface.