The pneumatic swivel unit is possible to perform repetitive moving work by rotating the rotary actuator while the pneumatic chuck is fixed to the object. Gears are formed in the rack piston, so that the driving shaft, in which the pinion gear is formed, rotates due to the reciprocating motion of the rack piston. The wear of the rod seal results in a loss of independence between the hole and the hole in the driving shaft, resulting in a leakage failure. In this paper, a life test method to reproduce the main failure mode of this swivel unit was developed and a reliability evaluation method of the swivel unit was established by selecting the comprehensive performance test, the environmental test and the safety test items. The life test method was based on the actual conditions of use, and the whole swivel unit was subjected to a straight-chuck-backward-rotation cycle as one cycle. Six samples were tested at a reliability level of 70% and a failure-free life test of 1.54 million cycles.