The invention relates to a liquefied natural gas carrier B type independent liquid cargo tank thermal insulation system with a sealing secondary screen wall. The liquefied natural gas carrier B type independent liquid cargo tank thermal insulation system comprises a thermal insulation layer, wherein the thermal insulation layer comprises a splash-proof screen, a secondary screen wall layer, a thermal insulation plate, an upper plate piece and a protection layer, the secondary screen wall layer is continuously bonded on the upper surface of the splash-proof screen, the thermal insulation plate is arranged between the splash-proof screen and the upper plate piece in a clamped mode, and the protection cover covers the outer surface of the upper plate piece. The thermal insulation layer of the thermal insulation system is continuously installed on and fixed to the periphery of a liquid cargo tank main screen wall, so that a thermal insulation enclosure layer for an LNG liquid cargo tank is formed. By means of the structure of the thermal insulation system, it is ensured that a communication interval passageway is formed between the main screen wall and the splash-proof wall, and when leakage happens to the main screen wall, liquefied natural gas which leaks can flow into a collection container through an interval space. The thermal insulation system further comprises a fixing mechanism of the thermal insulation layer, wherein the fixing mechanism can stably support the whole thermal insulation layer and fix the whole thermal insulation layer to the main screen wall.