The invention discloses a winding wire fixed type fuel assembly for a high-power density reactor core and a lead-base reactor. The fuel assembly comprises a plurality of fuel elements, positioning winding wires and an outer sleeve, wherein the plurality of fuel elements are regularly ranged to form a rod beam grid cell flow channel; the outer sleeve coats outside the plurality of fuel elements for restraining the flowing of a cooling agent; gaps among the fuel elements are fixed through the positioning winding wires; a fin wall surface is arranged at the inner side of the outer sleeve; fins are arranged to be right positioned in a middle position between the two adjacent edge fuel elements and are used for reducing the edge channel area. The rod beam grid cell flow channel is fixed by the winding wire, so that the dense rod beam arrangement can be realized; the high-powder pile neutronics requirement is met; the peripheral rod winding wire diameter is reduced, so that the goal of tightening the outer sleeve is achieved; the edge channel flow rate of the fins is restrained through the fins; the flow rate distribution in an assembly is optimized; the cooling efficiency of a cooling agent is improved; the rigidity of the outer sleeve is enhanced through the arrangement of the fins.