LNG ship filling system and method based on BOG reliquefaction

The invention provides an LNG ship filling system and method based on BOG reliquefaction, and relates to the technical field of clean energy. The filling system comprises an LNG power-driven ship storage tank, an LNG ship filling device and a BOG reliquefaction device. An outlet of the LNG ship filling device communicates with a liquid inlet of the LNG power-driven ship storage tank. The BOG reliquefaction device comprises a heat exchanger, a surge tank, a gas-liquid separation tank, a vaporizer, a self-pressurization heat exchanger and a liquid outlet valve, a gas outlet of the heat exchanger is communicated with the first end of the first pipeline, the vaporizer is connected to the first pipeline in series, and a liquid outlet of the heat exchanger is communicated with a liquid inlet of the gas-liquid separation tank through a second pipeline. According to the LNG filling system, the multiple tank cars are adopted for filling medium-large LNG ships at the same time, BOG generated during filling is liquefied