The invention belongs to the field of underwater electrical equipment and specifically discloses a natural convection and heat dissipation type underwater transformer. The natural convection and heat dissipation type underwater transformer comprises a shell body, a transformer body and a convection and heat dissipation assembly, wherein the shell body is of a cavity structure with a sealed upper end and an opened lower end and the lower end of the shell body is connected with a base; a sealed space which is fully filled with transformer oil is formed between the base and the inner part of the cavity structure of the shell body; an outer side face of the shell body is connected with a compensator; the transformer body comprises an iron core assembly, an input end and an output end; the iron core assembly is arranged in the sealed space and is mounted on the base; the input end and the output end of the transformer are arranged on a side wall of the shell body; the convection and heat dissipation assembly comprises a plurality of convection and heat dissipation pipes which are arrayed in the circumferential direction and are arranged around the outer part of the shell body; each convection and heat dissipation pipe is vertically arranged and two ends of each convection and heat dissipation pipe are connected with the shell body so as to be communicated to the sealed space. By adopting the natural convection and heat dissipation type underwater transformer disclosed by the invention, the problem of an existing heat dissipation manner that the heat dissipation efficiency is low is solved; the natural convection and heat dissipation type underwater transformer has he advantages of long heat exchange time, great heat transferring amount and high heat dissipation efficiency and is suitable for an underwater oil and gas production system.