Abstract: The vigorous development of China's mariculture industry has led to an increasingly urgent demand for high-performance auxiliary vessels. Taking a multi-functional aquaculture auxiliary catamaran as the research object, this paper uses the boundary element numerical method based on three-dimensional potential flow theory for numerical prediction. It presents the numerical simulation results of the catamaran's motion responses and the surface elevation between hulls under various loading conditions, sea states, sailing speeds, and wave directions, aiming to reveal its motion response patterns under complex sea conditions. The results indicate that under sea states 2 and 3, the seakeeping performance of the catamaran consistently showed the characteristics of being worst under light load, best under full load, and intermediate under half load. Wave direction had a significant impact on motion responses of the catamaran, with beam seas being the most unfavorable condition, leading to a significant increase in roll amplitude. The variation in ship speed exerted distinct effects on the motion responses in all directions under sea states 2 and 3, but its influence was limited under beam sea condition. The characteristics of surfaceelevation were significantly affected by draft, wave conditions, and speed. An increase in speed caused the resonant frequency at the peak of surface elevation to shift towards higher frequencies, while a decrease in draft could lead to significant surface elevation under specific coupled conditions of speed and wave state. Therefore, when sailing in light load condition, the catamaran should carefully plan its route and speed to avoid excessive motion responses and surface elevations.