Abstract: By comparing and analyzing 3 kinds of pig launching techniques, namely underwater pig launching, platform piglaunching and loop line pig launching, it is concluded that underwater pig launching is more suitable for the development ofunderwater marginal oilfields. The underwater pig launching unit used to store pigs and control the launch order of pipelinepigs is made up of junction device, pipeline pig storage bin and control system. The progress in pig launching units athome and abroad is investigated, and the applicable conditions and key techniques problems of the vertical and horizontal underwater pig launching units are summarized. The authors put forward solutions for the problems such as simplifying thestructure of underwater pig launching unit, optimizing control method, and reducing underwater operation steps of ROV, etc.