Abstract: The connecting union is a critical component in oil and gas fracturing operations, used to connect fracturing pumps, high-pressure manifolds, elbows, and valves to meet field installation requirements. However, leaks and fractures that occur during its service significantly affect production and even endanger personnel safety. Therefore, conducting failure analysis of the connecting union, exploring its causes of failure, and ensuring the safety and efficiency of fracturing operations are of great importance. This paper combines macro and micro failure analysis methods, mechanical property tests, and simulation analysis to conduct a failure analysis of the high-pressure manifold connecting union used in a fracturing pump in a Xinjiang oilfield. The results show that the failure mode of the connecting union is brittle fatigue fracture of the threaded part. The fracture surface of the failed part exhibits three typical characteristics of fatigue failure, with no signs of plastic deformation. The causes of failure are: ① The content of C, Cr, and Ni elements in some connecting unions does not meet standard specifications, and the yield strength, tensile strength, Charpy impact energy, and hardness mechanical properties are below standard requirements; ② High internal pressure and preloading cause high stress and large stress concentration areas at the threads of the connecting union; ③ Mechanical vibration and fluid pulsation act together over the long term. Finally, the paper proposes ideas and methods for structural improvement and material selection. The research findings have high engineering application value and guiding significance.