Objective To research into the etiology of carpal tunnel syndrome and seek for the best therapy.Methods The internal pressure of carpal tunnel above and under transverse carpal ligament were measured by blood pressure monitor and the thickness of transverse carpal ligament was observed.Results The internal pressure of carpal tunnel was(1.39±1.14)mmHg and(1.81±0.72)mmHg above the ligament while it was(3.02±1.12)mmHg and(3.15±1.23)mmHg below the ligament.The thickness of transverse carpal ligament was(0.13±0.06)mm.No results of internal pressure could be detected by this blood pressure monitor after cutting off transverse carpal ligament.Conclusion The internal pressure of carpal tunnel is connected with the thickness of transverse carpal ligament.The factor that makes transverse carpal ligament thicker is one of the inducing factors of carpal tunnel syndrome.