Abstract: The probability of LNG leakage out of the ships in a tunnel and the consequences are estimated quantitatively. The fault tree analysis is used to calculate the leakage probability and the consequences are modeled and simulated by means of Fluent. The research finds that the probability of accident for LNG ships is less than 1.00×10^-5, well under acceptable level. But the simulations indicate that the consequences could be extremely serious if a leakage does happen. The most dangerous consequence is fire, which will endanger an area up to 609 m²; The area causing people suffocating is the least, only 0.008 m²; The coverage of explosion is in between. As one may expect, the bigger the size of leakage hole, the more serious the accident and good ventilation can effectively alleviate the danger.