Gravitational desalination is an important sea ice desalination method. It essentially makes use of the different freezing points of a brine and pure water to promote the separation of the brine and fresh water ice crystals. The ambient temperature influences the ice temperature, which leads to a long desalination cycle and a low production efficiency. Aiming to solve the above-mentioned problems, experiments were designed considering different microwave powers, salinities, and sea ice masses and the physical properties of sea ice and microwave heating characteristics. The results show that the desalination rate of sea ice is the highest after 2-4 min; the desalination rate reaches up to 90% at a loss rate of < 40% when sea ice with a salinity of 5 parts per thousand is heated for 8 min in a 600 W microwave. Heavier sea ices need more time to completely desalinate. At lower microwave energies, sea ice can melt brines with higher salinities.