The reservoir of Kelasu gas field belongs to ultra-deep fractured low porosity sandstone. The reservoir matrix is the main storage space, and the multi-scale fracture system developed inside the reservoir is the main flow channel. The study area includes Dabei 9, Dabei 11 and Dabei 12 gas reservoirs located in the west of the Kelasu gas field, with near plane positions and highly consistent matrix properties, but there are significant differences in production dynamics and flow characteristics. Through the analysis of the production data and well test data in the study area, it is concluded that the different flow characteristics are caused by the difference of fracture system heterogeneity. In this paper, the pressure historical curve and the absolute value of the pressure derivative are used to identify the heterogeneous characteristics of reservoir fracture system. Two representative fracture composite pattern and flow models are proposed. The numerical well test models are established to verify effectiveness of flow model and analyze the sensitivity parameters. This study found that both large fractures controlled reservoirs and fracture networks controlled reservoirs can achieve high production in the Kelasu gas field, but gas wells in large fractures controlled reservoirs often quickly product water under the same production allocation conditions. With the development of Kelasu gas field, the non-uniform water cut of the reservoir leads to the number of water-producing gas wells increased rapidly. This has become the biggest challenge for gas field development. The early identification of reservoir heterogeneity through the well testing methods proposed in this article has strong reference significance for gas field development policies and water prevention strategies.