The invention belongs to the technical field of aircraft airtight frame structural design and particularly relates to a metal spherical frame and a design method thereof. The metal spherical frame comprises a spherical skin (1), a plurality of circumferential crack-arresting belts (2), a plurality of radial crack-arresting belts (4) and a butt joint piece (5), all of which are made of metal materials, wherein the spherical skin (1) is of a shell structure in a spherical crown shape, the circumferential crack-arresting belts (2) and the radial crack-arresting belts (4) are arranged on the spherical skin (1), the butt joint piece (5) is of an annular frame structure, and the spherical skin (1) and a fuselage wall panel are in butt joint through the butt joint piece (5). According to the method, a traditional panel airtight frame is designed into a spherical airtight frame, the spherical airtight frame is in the spherical crown shape, therefore, stress is more reasonable, and the structural weight of the airtight frame is greatly reduced.