Abstract: In the process of natural gas development, it is easy to cause serious plugging and throttling, which seriously affects the normal production of gas wells. By means of chemical capacity method, X-ray diffraction, infrared spectrum analysis, scanning electron microscope and energy spectrum analysis, the composition properties and formation mechanism of wellbore plug in gas well are studied. The results show that the wellbore plugging is mainly composed of CaCO_3, Fexsy, FeCO_3 and the heavy component of corrosion inhibitor. The formation mechanism is that the inorganic plug which corrodes and scales acts as the skeleton, the organic plug which enters the well acts as the filler, forming a dense mixture with high viscosity and no gap between them, which provides a basis for inhibiting the formation of plug and taking effective measures to remove the plug.