The low pressure ammonia liquor is mainly used for cooling crude coke oven gas,once it is cut off,the production would be seriously affected.The replacement of the LP ammonia liquor valve is very risky,in particular more difficult for replacing the main pipe valve.In this paper,a method of on-line replacing LP ammonia liquor valve is introduced,which not only ensures the GCM temperature is controllable in fluctuation,but also effectively avoids potential bleeding of crude gas and avoids damage to crude gas transferring device during the replacement.