Armored face conveyor works in bad environment. Its floating oil seal installed in sprocket assembly is always failed and causes oil leakage, which may cause the lubricating oil waste and pollute the work environment, and even cause the damage of the bearing inside sprocket assembly. Various factors caused seal failure were analyzed from the quality of sprocket assembly floating oil seal, component installation, the habits of users and other aspects. It has a certain reference role to improve the seal reliability in sprocket assembly.