In order to take quick and effective measures for preventing fire and explosion caused by unloading arm leakage, feasible contingency plan must be developed. Conducted is analysis on the change of physical characters of LNG which leaks into the ground and sea and calculated is leakage amount after leak source is cut off the results show that the leakage amount may reach up to 324.3kg in a short time and the potential harm is extremely great. Such contingency measures for unloading arm leakage are clearly put forward as judging the leakage amount, conducting process isolation rapidly, cutting off the leakage source, controlling LNG volatile and reducing LNG concentration. In order to prevent leakage during LNG unloading, unloading preparation and procedure must be strictly followed and unloading operation shall be implemented in absolutely safe conditions.