A scatterer-size gradient photonic crystal flat lens is proposed， which can simultaneously realize point source imaging and plane wave focusing in TM and TE polarization modes，and both imaging and focusing break through the diffraction limit in TM polarization mode，and realize sub-wavelength imaging and focusing in TE polarization mode. This flat lens can realize polarization-insensitive imaging and focusing without any additional polarization components. It is expected to be used in the design of multi-functional optical polarization-insensitive imaging and focusing devices， and can be applied to real-time biological display， high-density optical storage and microelectronic lithography， and improve the application potential of gradient PC flat lens.