Fluid accumulation in the subacromial bursa may be caused by long-term labor injury and degenerative disease of the shoulder joint. 1. Long-term strain: the subacromial bursa is located between the shoulder joint capsule and the rostral prominence. Long-term heavy physical labor of the shoulder joint may cause repeated friction and impact between the joint capsule and the surrounding soft tissues, resulting in aseptic inflammation, which leads to an increase in exudation from the joint capsule and the surrounding soft tissues, and impaired blood circulation locally, so that exudate cannot enter the blood circulation in time, resulting in the appearance of effusion in the subacromial bursa. 2. Degenerative disease of shoulder joint: when degenerative disease of shoulder joint occurs due to various reasons, it will lead to abnormal functional activities of shoulder joint and decrease of joint stability, etc. In order to fight against the instability of the joint, osteophytes, synovial hyperplasia, and release of more joint fluid for lubrication will occur, which may also occur. There may be other reasons for the fluid accumulation in the subacromial bursa, so it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of the doctor.