The invention discloses a noise reduction structure of a chimney of a gas boiler. According to the noise reduction structure of the chimney of the gas boiler, the outer wall of the chimney is sequentially covered with a damping plate, a rock wool plate, centrifugal glass wool, glass fiber cloth and a protective plate from inside to outside. The thickness of the damping plate is 5-7 mm. The thickness of the rock wool plate is 60-70 mm. The thickness of the centrifugal glass wool is 60-75 mm. The thickness of the glass fiber cloth is 3-4 mm. The thickness of the protective plate is 0.6-0.9 mm. The noise reduction structure of the chimney of the gas boiler is good in damping and noise reduction effect and low in cost, binding is convenient when noise reduction is conducted on the chimney, and the noise reduction structure can be widely applied to noise reduction of chimneys of gas boilers of various types.