The invention discloses an offshore LNG receiving system and method. The system comprises a full-cooling type LNG transport ship, an LNG receiving device, an LNG pressurizing gasification system, a natural gas cooling system, a cold-insulation circulating system and a ship-shore connecting system. The floating type or gravity base type offshore LNG receiving system is constructed at an offshore position to rewarm imported liquefied natural gas, the liquefied natural gas is conveyed to a natural gas trunk line through a single-point mooring device and a submarine pipeline to be received at the offshore position, and therefore the problem that the address of a dock for an LNG receiving station is difficult to select is solved. A shore-based LNG receiving and gasifying function is changed to be achieved at the offshore position, and therefore occupied port shoreline resources are reduced. Compared with a traditional dock loading technology, the offshore LNG receiving system is quite suitable for regions lacking natural ports and the condition that a port plan is difficult to change, the technology is simple, investment is low, the construction period is short, and if market changes, equipment can be transferred to other regions for continuous service.