To ensure the safety of liquefied natural gas (LNG) transportation, a helium mass spectrometry (HMS) based leak detection study was conducted on a simulated model of a Mark III LNG vessel. Three leaks with varying leakage rates were embedded in the simulated model. The study investigated the effects of different sweep speeds and distances of the suction gun on the leak detection results by injecting a specific concentration of helium gas into the model. The results indicated that for a high leakage rate (on the order of 10_-5^Pa.m3/s), the sweep speed had minimal impact on the measured leakage rate, and the sweep distance had a negligible effect on the leak detector readings. However, for a leakage rate on the order of 10_-7^Pa.m3/s, the readings significantly decreased with increasing sweep speed. Additionally, the readings rapidly dropped to the background value and became unreadable as the sweep distance increased. Thus, conducting leak detection at the smallest possible sweep distance is recommended for obtaining more reliable data.