The boil off gas from LNG storage tank will be multistage compressed to above 20MPa, and the compressed gas ingress into the cryogen-ic cold box, where it will be pre-cooled by the boil off gas from LNG storage tank. Then the high pressure and cryogenic gas will be expand-ed in the ejector and the mixture of gas and condensate will be generated in the 1st condensate receiver, the condensate will be separated and goes into 2st condensate receiver and then return to the LNG storage tank. LNG storage tank's boil off gas will be drown out by the ejector's vacuum nozzle and flow into gas booster compressor for the next compression refrigeration cycle.