Based on the reported physical experiment, the dynamic response of T-shape pipe and fluid transient is simulated through the arbitrary Lagrangian-Eulerian (ALE) finite element method. The simulation results and experiment data are consistent. It proves that the ALE finite element method can be applied in modeling the water hammer. Based on this, more detail study about the T-shape pipe and dynamic hoop stress during the water hammer are carried out. The maximum hoop stress in the process is equivalent to 1.3~1.7 times the stress that would be expected if an equivalent static water pressure is applied to the inner wall of the pipe. The periodicity of dynamic hoop stress is same as the water hammer pressure. This conclusion is same with the result of straight pipe too.