Disclosed herein are a fuel nozzle of a gas turbine combustor for dimethyl ether (DME, CH3OCH3) and a design method thereof. The fuel nozzle includes a pilot fuel injection hole formed at the center of the nozzle and a plurality of fuel injection ports formed at equiangular positions around the pilot fuel injection hole to inject DME. Each of the fuel injection ports includes a pair of upper and lower DME injection orifices communicating with a fuel-air mixture injection swirler. The upper DME injection orifice becomes gradually wider, whereas the lower DME injection orifice becomes gradually narrower. Thus, DME can be optimally combusted in the gas turbine combustor, thereby achieving cost reduction of power plants, enhancement in reliability of the power plants, and diversification of usable fuel.