Tight sandstone gas reservoirs are important component of unconventional oil and gas resources in China. Tight gas accumulation and key target optimization are affected by reservoir heterogeneity, which in turn restricts the efficient development of gas field. This study aims to investigate the characteristics and formation of reservoir heterogeneity. Taking reservoirs of the 1st Member of Shanxi Formation and the 8th Member of Shihezi Formation in the southwestern Sulige gas field as examples, based on core analysis, scanning electron microscopy analysis, thin section identification, production data, and logging data analysis, the heterogeneity characteristics and gas- water distribution are analyzed, and the influences of sedimentation and microscopic pore evolution on tight gas reservoir are discussed. The results show that reservoirs in southwestern Sulige gas field have strong heterogeneity. Heterogeneity is mainly manifested by vertical rhythm of grain size, uneven distribution of interlayer, and permeability differences in reservoir. Heterogeneity is also influenced by sedimentation and diagenesis. Sedimentation controls the hydrodynamic condition, distribution, thickness and superimposition patterns of sand bodies. Microscopic heterogeneity is influenced by sandstone composition and pore evolution. The heterogeneity and gas- bearing distribution of tight reservoirs in the Sulige area are controlled by the composite sand body with different thickness and superimposition patterns, the sandstone composition, pore- throat structure, and the selective charging of tight gas. The high porosity and permeability of the composite sand body is the sweet spot of tight gas. However, attention should not only be paid to the thick sand body with high porosity and permeability, but also to the small- scaled lenticular sand body with strong heterogeneity when optimizing target area. The influence of reservoir heterogeneity on gas- water distribution and hydrocarbon accumulation should be fully considered in tight gas production.