The utility model relates to a device for fatigue test of a deepwater riser, which is characterized in that the device comprises a main cylinder, two axial load cylinders, a riser test sample assembly, transverse servo load cylinders and soil body action servo load cylinders, wherein an external pressure interface and an air relief valve are arranged at the top of the main cylinder; the two ends of the main cylinder are connected with the two axial load cylinders, of which each has an axial force interface respectively; the two ends of the riser test sample assembly are hinged on the pistons of the axial load cylinders on the corresponding sides respectively; the riser test sample assembly comprises a test sample body and a connecting rod; a simulated soil body is arranged below the test sample body; two internal pressure interfaces are arranged at the two ends of the test sample body; a plurality of sensors are arranged on the test sample body, and the test lead wire of each senor passes through the main cylinder and then connects with a testing device; the individual transverse servo load cylinders and the individual soil body action servo load cylinders are all arranged on the main cylinder, the pistons of two of the transverse servo load cylinders are butted against the top of the test sample body, and the piston of the other transverse servo load cylinder is butted against the bottom of the junction of the test sample body and the connecting rod; and the pistons of the individual soil body action servo load cylinders are butted against the bottom of the simulated soil body.