The invention belongs to the technical field of nuclear reactor fuel, and particularly relates to a test device for metal material creep under the in-reactor radiation environment. The test device comprises a thin-walled circular pipe, a mandrel, a first end plug and a second end plug, the first end plug and the second end plug are fixedly connected with the upper end and the lower end of the thin-walled circular pipe correspondingly, the mandrel is arranged in the thin-walled circular pipe, one end of the mandrel is fixedly connected with the first end plug, gaps exist between the other end of the mandrel and the thin-walled circular pipe as well as between the other end of the mandrel and the second end plug, and the thin-walled circular pipe is pre-filled with pressure inert gas. The test device is simple in structure, convenient to realize and feasible in manufacturing, and the demands of cladding material creep test research and data acquisition under the irradiation environment in a test reactor and a commercial reactor can be met.