In this paper, a 2D photonic crystal (PC) with negative refractive index at multi-band is designed. Plane wave expansion method (PWEM) is used to obtain the band diagram and the equal-frequency surface (EFS). And the finite difference time domain (FDTD) simulation method is also used to analyze the equivalent refractive index of the PC. The results from both methods show that the equivalent refractive index of the PC at specifical band is negative.