In order to study the failure reason of the doublepump of a feedwater pump unit turbine, the double pump was disassembled and inspected. It was found that the shaft was broken, and the bearing and the connecting parts of the shaft were also damaged in different degrees. The main damaged parts of the doublepump were macroscopically inspected, the chemical composition, metallographic structure, mechanical properties and fracture morphology of the broken shaft were systematically analyzed, and the failure analysis and calculation of the shaft, key, bearing and other parts were carried out. The results show that the axial preload of the doublepump bearing is too large, which reduces the working life of the bearing, causes contact fatigue failure and the shaft tilt, makes the rotor on the shaft stuck, and finally the shaft is twisted off due to excessive load. The research results can provide reference for analyzing the similar shaft fracture cause.