In this paper, we present the effect of grating structure on Relative Intensity Noise (RIN) in Distributed Feedback (DFB) laser diode. We analyze the noise in three types of grating shape including longitudinally uniform, concave and convex depth. It is shown that the concave grating against uniform and convex structure is suitable for reducing the Spatial Hole Burning (SHB) effect, but is not appropriate for low noise DFB lasers. According to the results of analysis, in uniform grating, RIN decreases when the corrugation depth increases. In concave and convex structure, grating depth is composed of fixed and variable parts. When fixed part of grating depth is constant, increasing variable amplitude of grating reduces RIN and when the variable part of grating is constant, increasing fixed part of grating reduces RIN. In all of the three type structures, RIN for the symmetric grating is lowest. Also with decreasing RIN, relaxation oscillation frequency decreases and when the SHB effect occurs, the rate of this decreasing is low. We conclude a special shape of grating that has low SHB effect and low noise in optical communication systems.