The origin of the pectoralis major muscle is located on the medial half of the clavicle, the sternum, and the anterior wall of the superior 5-6 costal cartilages and rectus abdominis sheath. The pectoralis major muscle is located in the superficial upper part of the anterior thorax. The starting point is located on the medial half of the clavicle, the sternum and the anterior wall of the superior 5-6 costal cartilages and the rectus abdominis sheath, and ends at the crest of the greater tuberosity of the humerus. The muscle belly of the pectoralis major is fan-shaped and concentrates outwardly and superiorly to terminate at the crus of the greater tuberosity. The structural characteristics of the pectoralis major muscle include different starting points of the fibers have different stops, the fibers of the clavicular region form the anterior layer of the flat tendon outwardly, the fibers located in the lateral part of the fibers stop at the upper end of the lateral lip, the fibers of the medial part of the fibers stop at the lower end of the lateral lip, and the fibers of the abdominal and thoracic ribs are located in the clavicular part of the fibers of the posterior and lower part of the clavicular fibers. The main function of the pectoralis major is to make the upper and lower muscle bundles have the same degree of extension when the upper arm is abducted. Contraction of the pectoralis major allows the humerus to be adducted and rotated inward, the pectoralis ribs allow the lifted upper extremity to be extended posteriorly to aid in respiration, and contraction of the clavicle allows the shoulder to be flexed. When discomfort occurs, medical attention should be sought promptly to avoid delaying the condition.