In order to optimize the performance of gratings,one cladding-modulation grating with an asymmetric structure is proposed based on the complementary metal oxide semiconductor compatibility fabrication technique. By adjusting the position of grating teeth, the coupling efficiency of the transmission light in the waveguide is altered, which eventually achieves the improvements of reflection bandwidth, extinction ratio and output power of the grating. The effect of the improved grating structure on coupling coefficient, reflection bandwidth and output performance of gratings is analyzed by using the coupled mode theory, and the numerical simulation is conducted as well with the finite element method. The results show that the reflection bandwidth of the improved grating is reduced from 0.9 nm to 0.3 nm, the absolute value of the extinction ratio is increased from 29.2 dB to 35.1 dB, and the optical power dissipating in the claddings is decreased from 5.99×10-5 W to 3.13×10-5 W. The performance of the improved grating device is improved.