In view of the operation status of lap adhesion of flexible secondary insulation in plane area of Mark Ⅲ liquid cargo containment system of Liquefied Natural Gas (LNG) carrier, the certification flow, operation flow, and lap adhesion quality inspection of traditional lap adhesion process are analyzed, and the operation flow of traditional lap adhesion process is optimized. An improved lap adhesion process which can effectively increase the operation efficiency of lap adhesion of flexible secondary insulation in plane area is proposed, and its advantages are summarized, which is of certain reference significance for the construction of LNG carriers.