Abstract: As more and more mining of acidic gas reservoir, downhole corrosion prevention and corrosion monitoring are increasingly important. The traditional downhole coupon corrosion monitoring is to hang a piece of coupon installed inside a stationary tubing nipple, but the coupon must be into and up with the tubing in the well. Because the monitoring depth is fixed, the result and analysis of downhole coupon corrosion monitoring are limited by the workover job opportunity. Aiming at the faults of conventional downhole corrosion monitoring as well as the demand of current locale monitoring, a tool for gas well downhole corrosion monitoring was researched and developed independently. The result of indoor evaluation and field test indicated that the tool has the advantages of reliable performance and convenient implement, more real and intuitive evaluation of downhole corrosion, a wide practical range, as well as convenient adjustment for the depth of corrosion monitoring, adjustable number and type, etc. The successful application provides a direct basis for the downhole corrosion inhibition of gas wells and selecting reasonable workover job opportunity, greatly reduces the cost of downhole corrosion monitoring of gas well and overhaul operations, which has an important meaning for gas well safety production.