A plug member of gas valve has an axial bore, a first bore, and a second bore, wherein the first bore and the second bore are located in a radial direction of the plug member, and communicate with the axial bore, respectively. A diameter of the first bore is larger than that of the second bore. A first guiding slot and at least one first oil groove are recessed into the outer peripheral surface of the plug member, wherein the first guiding slot has a first end communicating with the first bore, and a second end near the second bore without physically communicating with the second end. The at least one first oil groove is near the second end of the first guiding slot without physically communicating with the first guiding slot or the second bore. Whereby, the first oil groove provides space for receiving lubricant.