A composite wick structure of a heat pipe which is applied with a tube circumferential surface contacted to a heat source includes a plurality of grooves and a sintered-powder layer. The grooves are longitudinally formed on the internal sidewall of the tubular member. The sintered-powder layer filled in the grooves is attached to at least a portion of the internal sidewall of the tubular member. By the better capillary force provided by the sintered powder, the liquid-phase working fluid can reflow to the bottom side of the heat pipe quickly to enhance the heat transmission efficiency. Further, the problem caused by usage of an axial rod during the process of applying sintered powder can be resolved.