The invention discloses a liquefied natural gas filling system which comprises a filling pipeline, a filling stop valve arranged in the filling pipeline, a diffusing pipeline communicating with the filling pipeline, and a diffusing stop valve arranged in the diffusing pipeline, wherein ports in two ends of the filling pipeline are a first port communicating with a filled storage tank and a secondport communicating with a filling storage tank; and the connecting part of the diffusing pipeline and the filling pipeline is positioned between the filling stop valve and the second port. Compared with the prior art, the liquefied natural gas filling system solves the technical problems that application of liquefied natural gas is not economical and causes serious pollution to the environment caused by long filling time and large diffusing quantity of the existing filling pipeline.