Most photonic crystal lens based on square or triangular lattice usually uses high refractive index materials such as Si or SiO2. And the study on such lens has been focused on the infrared wavelength range. With the development of the visible light communication technology, the research of Sun-flower self-focusing lens with low refractive index materials in visible band becomes very meaningful. To meet that requirements, self-focusing lens based on Sun-flower shaped graded PC was proposed. Firstly, by comparing the convergence intensity of this proposed lens between TE-polarized and TM-polarized mode, the convergence effect of TM polarization was superior to the convergence effect of TE polarization. Then self-focusing flat lens based on TM mode Sun-flower graded PC was designed. The beat length of the flat lens was given by the simulation of optical field transmission. The layers of the flat lens were optimized, and the best number of the layers was 22. In the end, the influence of the number of columns was discussed. The results show that the intensity decreases as the number of columns reduces. It has great guiding significance to make optical integrated devices with high-performance convergence effect, short focal length and small volume.