The invention relates to a deep underwater wellhead fatigue test device which comprises a power and control system, a transmission system, a wellhead system, a data acquisition and processing system and a safety protection cover, wherein the data acquisition and processing system transmits the acquired state data of the wellhead system to the power and control system; the power and control system drives the control transmission system according to the received state data; the safety protection cover is arranged on the upper part of the wellhead system, and the transmission system is also positioned in the safety protection cover; the power and control system comprises a motor, a variable frequency controller and a computer; and the motor is connected with the computer through the variable frequency controller. The deep underwater wellhead fatigue test device disclosed by the invention is simple in structure, low in test energy consumption, high in test accuracy and excellent in safety performance, has excellent underwater wellhead fatigue test capacity and can be widely applied to fatigue tests of various deep underwater wellheads.