The southern Junggar Basin, a key strategic area for natural gas exploration and development due to its abundant hydrocarbon resources. However, it presents significant geological challenges, including ultra-deep reservoirs (>8000 m), abnormally high formation pressures (pressure coefficient > 2.16), and complex fluid identification. Such conditions have a critical impact on the safety, efficiency, and accuracy of gas well testing operations. To address these challenges, this study proposes an innovative dynamic analysis methodology specifically designed for ultra-deep, ultra-high-pressure gas wells utilizing limited early-stage test data. First, an approximate fluid density calculation method was developed for both well opening and shutting-in stages based on pressure balance principles, enabling rapid determination of formation fluid types. Second, productivity was comprehensively assessed using transient well testing analysis and well comparison techniques. Additionally, by utilizing production pressure differential and wellhead pressure as control indicators, a reasonable production range (defined by choke size) was determined, providing a robust technical foundation for safe testing operations. Field applications confirm the methodology's effectiveness in achieving both operational safety and accelerated testing. This approach offers valuable technical insights and establishes a replicable framework for similar reservoirs in deep petroleum systems.