The invention discloses a cod end structure for stationary net fishing gears and a mesh size-setting method thereof, which relate to a marine stationary fishing gear. The problem solved by the invention is to provide a method for determining the cod end structure of the stationary net fishing gear and the mesh thereof. The technical scheme of the invention adopts a stationary cod end, the cod end is characterized in that the cod end is rectangular, the cod end is of a four-piece structure, all the sides of which are symmetric, and knots are not reduced; the mesh size of the cod end, which corresponds to the characteristic lengths of main fish varieties, is inversively deduced with a linear functional equation (L50 equal to 3.174 multiplied by Me minus 29.436) which is established according to L50 and experimental mesh size, wherein L50 is the length value of a sexually mature body when the survival rate is 50 percent, and Me is the mesh size; and a transverse reinforcing bar which can be connected with floaters is added at the middle of the cod end.