The invention relates to a fatigue experiment device for a deepwater stand pipe, which is characterized by comprising a main cylinder barrel, an axial loading cylinder, a stand pipe test piece assembly, transverse servo loading cylinders and soil action servo loading cylinders, wherein the top of the main cylinder barrel is provided with an external pressure joint and an air vent valve; two ends of the main cylinder barrel are respectively connected with the axial loading cylinder with an axial force joint; two ends of the stand pipe test piece assembly are respectively hinged on a piston of the axial loading cylinder on the corresponding side; the stand pipe test piece assembly comprises a test piece body and a connecting rod, wherein simulated soil is arranged below the test piece body,two ends of the test piece body are respectively provided with an internal pressure joint, and the test piece body is provided with a plurality of sensors; a test lead of each sensor penetrates out of the main cylinder barrel to be connected with the test instrument; each transverse servo loading cylinder and the soil action servo loading cylinders are all arranged on the main cylinder barrel; the pistons of two transverse servo loading cylinders are supported on the top of the test piece body; the piston of the other transverse servo loading cylinder is supported on the bottom of the junction of the test piece body and the connecting rod; and the piston of each soil action servo loading cylinder is supported on the bottom of the simulated soil.