This case is utility model patent infringement dispute. The patented product is the muffler device for local ventilator used in coal mine. The disputed parts are called ring filter and round muffler，with different names and different materials，and the defendant argues with “prior art”. The court of first instance held that the infringement was not established，ruling that the plaintiff lost the lawsuit，while the court of second instance held that the infringement was established. The two trial courts have the same determination of the objective facts，but the difference lies in the understanding and application of the law and the judgment of the nature of the facts.