A hexagon accelerator driven subcritical reactor fuel assembly and a design method thereof are disclosed. The assembly includes a hexagon base the top surface of which is provided with a plurality ofbase units for fuel rod mounting, with one of the base units being at the center of the base, other base units surrounding the center base unit and being arranged in an annular array manner, distancesbetween adjacent base units being equal; a shell including a prismatic sleeve the cross section of which adapts to the shape of the base and the bottom of which is mounted on the base; an inner sleeve including a prismatic sleeve, disposed inside the shell with a gap between the inner sleeve and the shell, with the bottom of the inner sleeve being mounted on the base; and a plurality of fuel rods, wherein each fuel rod includes a cylindric casing and a core rod in the casing and made of fuel, the bottom of each casing is mounted in one base unit, and the number of the fuel rods is equal to the number of the base units. The assembly and the method are used for solving a problem that neutron performance is poor, and technical effects that economic performance and neutron performance are high are achieved.