Abstract: Due to sulfurization,hydrogen brittleness,and electrochemical corrosion,the casing of large size of old oilfields is worn and hence has a negative effect on the oil well production.Furthermore,it gets difficult to repair the casing of large size because of its serious damage,large span,and access to the ground.In view of this,the author in this paper analyzes the damaged causes and the limitations of conventional repairing technologies,studies and applies the repairing techniques of casing withdrawal-altering in,introduces such key techniques as the well-filling method,the cutting technique,the old technique of withdrawing casing,the dressing technique for facets,the butt joint technique for casing,and safety consideration by taking the repairing of the damaged casing of Well Taveira-6 as an example,and discusses the operation of withdrawal-altering in techniques and its effect in detail.This will be a good reference to the research on repairing techniques of upper damaged casing in the future.