Abstract:The problem of leakage existed in the main air blower motor oil seal in heavy oil fluid catalytic cracking unit was analyzed,the main reasons that caused the large leakage of the oil seal were pointed out,such that the materials of the oil seal body,the oil seal and the tension spring can not meet the requirements,the oil flow between the bush and the oil seal is too large.Through improving the materials of the oil seal body,the oil seal and the tension spring,and improving the oil seal structure such as designing an oil retaining ring in the front end of the oil seal and adjusting the clearance between the bush and the oil seal,the problem of leakage of the motor oil seal was solved.