The transmission spectrum of a two- dimensional photonic crystal waveguide with edge defects of different refractive indexes (RIs) is analyzed, and accordingly a proposal to improve the sensitivity of RI sensor is put forward. The simulations and calculations show that the offset of the upper band edge of the transmission band is related to the RI of the analyte. For the same RI variation, the shift of the upper band edge of the transmission band can be greatly improved by changing the related geometrical parameters of holes at the defect area near both sides of the waveguide. Namely,the sensitivity of the RI sensor is enhanced. In this paper the sensitivity is respectively improved from 55 nm/RIU (RIU means refractive index unit) to 405 nm/RIU and 36 nm/ RIU to 222 nm/RIU corresponding to the range of the variation of RI (Dn) from 0.0 to 1.0 and 1.1 to 2.0 after the optimizing process.