Aimed at the problems of slag leakage, cracking, abrasion, etc., the technical retrofit of slag discharge system was implemented for the 300 MW circulating fluidized bed boiler (CFBB) in Xukuang Power Plant, which included the substitution of improved circular metal corrugation compensator for expansion joint, setting supporting structure at the joint of slag inlet pipe and furnace, setting wear-resisting structure at the target area of expansion joint of slag inlet pipe, setting wear-resisting box at upper and lower elbow of slag inlet pipe. Through the retrofit, the equipments service life could be prolonged, the maintenance cost could be reduced, and the safety coefficient of long period stable operation could be improved.