By integrating an electrostatic comb drive actuator with a Ⅲ-nitride grating, a Micro-electric-mechanic System (MEMS) tunable Ⅲ-nitride grating was obtianed on a silicon substrate to modulate the grating period. Firstly, the MEMS-tunable Ⅲ-nitride grating was designed on the basis of the Ⅲ-nitride-on-silicon substrate, in which the design values of grating period and the grating width are 1.1 μm and 0.8 μm, respectively. Then the Rigorous Coupled-wave Analysis (RCWA) method was used to analyze the optical responses of the Ⅲ-nitride grating under transverse magnetic modes. It shows that the resonance peak of the Ⅲ-nitride grating has a serious shift by changing the grating period and duty cycle. Finally, the MEMS-tunable Ⅲ-nitride grating was fabricated by combining an electron beam lithography, a Ⅲ-nitride dry etching and a deep silicon etching. Experimental results and rigorous coupled-wave analysis indicate that the fabricated MEMS-tunable Ⅲ-nitride grating has good quality and the shift of the resonant peaks is observed from 1.345 μm to 1 40 μm by applying a voltage on the electrostatic actuator. These results satisfy the requirement of modulating the optical responses of Ⅲ-nitride gratings by using MEMS technology.