The Well Ke-20 is a gas storage well located in the Kekeya condensate gas field. The cementing quality of the well section above the top boundary of the gas reservoir does not meet the requirements， and it needs to be resealed after casing forging and milling. Due to the deep forging and milling point， the high steel grade of the forging and milling casing， the insufficient construction displacement and pump pressure of the on-site equipment， the forging and milling tools cannot completely forge and mill the casing coupling， and the milling cutter tension is not enough， it brings about many difficulties for the forging and milling operation. After optimizing the forging milling tool sellection， designing the forging and milling construction parameters and drilling fluid system， increasing the displacement of the pump truck with the mud pump， polishing the forging and milling tool inhibiting device， and adjusting the viscosity of the drilling fluid funnel in stages， the forging and milling footage in a single drilling trip is 19.33m， the forging and milling speed is 0.48m/h， the cutting return rate is 71%， and the milling tool utilization rate is 90%. Compared with the previous drilling trips， the indicators mentioned above are increased by 55.5%， 26.3%， 9.2% and 26.3% respectively， and the forging and milling efficiency is improved effectively. Which provides an important experience reference for the efficient construction of other similar casing forging and milling wells.