Abstract: The semi-submersible vessel is designed as an efficient transportation specifically used to carry large-scale undividable integral equipment,which is regarded as the high-tech and high value-added vessel in the shipbuilding industry.This kind of semi-submersible vessel nowadays is rarely in service worldwide.The ＂Development Way＂ identified so far as such kind of semi-submersible vessel was the first self-propelled vessel in the e world which was originally converted from a LPG carrier.Many restrictions imposed on the conversion activities of such LPG carrier due to lack of relative reference and experiences on the design.This paper presents a description of this conversion designed LPG carrier with respect to the main technical performance and features,together with the aspects including general arrangement,structure strength,stability and design difficulties facing in the conversion design.