Abstract: In order to study the effect of strata thickness on the fracture development in sand-mud interbed, this paper took the sand-mud interbed reservoir of braided river delta front in Keshen gas field in Tianshan mountain piedmont as an example, analysed the generation mechanism of structural fractures, calculated the density, aperture and porosity of fractures by using numerical simulation method, and then proposed six models for fracture development in the sand-mud interbed. The simulated results show that the thinner the single thickness of sandstone or mudstone, the easier the fracture generation, also, the fracture development of the interbed is influenced by the strata thickness. In the condition of same stress, the fractures with large aperture and long extension may occur in medium-thick（1.5~10 m）sandstone, and be able to extend to or penetrate the mudstone. The fractures in thin (less than 1.5 m) sandstone with small aperture have weak effect on the mudstone. For mudstone of same thickness, the thicker the sandstone in it, the easier the fracture generation, and when the mudstone is less than 1 m in thickness, the loaded mudstone is easy to rupture and generate fractures by itself. In the area with similar regional tectonic deformation, the underwater distributary channels in braided river delta front are of high fracture porosity and good connectivity and could form good reservoirs, followed by mouth bar, distal sand bar, sand sheet and underwater interdistributary sands, they have low fracture porosity and low connectivity, being difficult to become favorable reservoirs. When the mudstone reaches 1 m and its sandstone is less than 5.5 m in thickness, it could become the barrier, enough acting as an effective sealing to oil and gas