For fishery vessels, once the ammonia in the cabin leaks and spreads, it will cause serious environmental pollution and casualties. Therefore, the ammonia leakage detection device is installed for detecting. Since it is not easy to move the installed detection device, the installation position needs to be considered properly in advance. Based on the Fluent software, the numerical simulation of ammonia leakage in the freezing cabin of the fishery vessel is carried out to study the concentration changes of ammonia in the cabin in different leakage directions and positions. The results show that the change of the leakage direction has little effect on the ammonia detection at the monitoring points near the top of the cabin and the bulkhead. The change of the leakage position has a great effect on the ammonia detection at the monitoring points. The ammonia detection at the monitoring point in the higher position is more accurate. After the ammonia leaks and spreads, the concentration is high near the bulkhead and the top of the cabin. Therefore, the ammonia leakage detection device is preferably to be installed in the upper position of the freezing cabin, and detection devices is required to be arranged near the top of the cabin and the bulkhead to determine whether the ammonia leaks.