Abstract: In order to solve the pigging problem of deep-water subsea pipeline, in line with the pigging principles of subsea pipeline, a new type under-water pig launch device is designed to effectively avoid the problems of pig receiving and pipeline shutdown caused by platform launch device. The structure of under-water pig launch device has been designed in detail, mainly including connector, protection frame, main launch structure, upper open-close mechanism and valve control system. This paper also introduces the workflow of under-water pig launch, introduces the advantages of this device compared with the traditional one, and finally presents numerical analysis on two key parts, the claw connection flange and ball storage cylinder, and the results show that it meets the design requirements. This device provides a new effective way to the pigging of deep-water pipeline.