The utility model belongs to electrical equipment field under water to specifically disclose a natural convection heat dissipation formula is transformer under water, it includes casing, transformer body and convection subassembly, and the casing seals lower extreme open -ended cavity structure for the upper end, and its lower extreme links to each other with the base, and the base forms an airtight space that is full of transformer oil with the inside of casing cavity structure, and the casing lateral surface is connected with the compensator, the transformer body includes iron core subassembly, input and output, and the iron core subassembly is located in the airtight space and is installed on the base, and input and output setting are on the casing, the convection subassembly encirclesat the outside a plurality of convection pipes of casing including being circular arrangement, every vertical the arranging of convection pipe, and both ends link to each other in order to switch on with airtight space with the casing. The utility model discloses can effectively solve the low problem of current radiating mode radiating efficiency, have the advantage that heat exchange is chronic,the heat transfer capacity is big, the radiating efficiency is high, be applicable to oil and gas production system under water.