In order to make clear the cause of interlock shutdown at LNG filling station due to insufficient cavitation allowance of submerged pump, established is the LNG filling station cavitation allowance model and analyzed is the cause of submerged pump cavitation allowance drop. Fast pump tank temperature rise results in rapid increase of LNG saturated steam pressure at the pump inlet and the damaged temperature gradient in LNG storage tank results in tank pressure drop, which are the main reason for submerged pump cavitation allowance drop. It is pointed out that heat preservation, regular LNG replacement of pump pool and decompression flash can lower the temperature in pump pool, LNG tank temperature gradient increase can raise tank pressure and timely tank LNG supplement can increase hydrostatic pressure and cavitation allowance of submerged pump can be increased through these processing measures.