Objective.To observation the change of thyrohyoid muscle(THM)after recurrent laryngeal nerve(RLN)has been cutting off.The animal experimental results were reported.Method.The animal experimental model of RLN paralytic was completed in 9 dogs.The specimens of THM were treated by histochemiscal staining after 2,4,6,8,10,20 day operation respectively and the diameter and areas of three types muscle fibers were determined by microscope.Results.The diameters and areas about 3 types muscle fibers of THM descended after operation,the value of them reached the minimum simutaneously,then recovered step by step.Conclusion.The changes of THM was related to operative trauma and nutrition disorder probably,while it was not related to RLN cutting.