The invention discloses a specimen holder of a tube or a bar for a tension test. The specimen holder comprises a tension handle, a locking part, a holding seat and a holder body, wherein the holder body comprises a cylinder body and a circular truncated cone body which are integrally formed; the maximum external diameter of the circular truncated cone body is greater than the external diameter of the cylinder body; the whole circular truncated cone body is provided with at least two grooves along the axial direction, and the two grooves are used for segmenting the circular truncated cone body into holding blocks; a holding part for holding a test specimen is arranged on the inner surface of each clamping block; the holding seat sleeves the outside of the holder body and is connected with the holder body in a matching way; the holding seat is provided with a first conical surface matched with the circular truncated cone body; the front end of the locking part is connected with the holding seat through a spiral structure; the tension handle is connected with the rear end of the locking part. The specimen holder disclosed by the invention is small in size, convenient in disassembly and assembly and uniform and reliable in holding force; the specimen holder realizes automatic centering in a clamping process, is uniform, quick and reliable in clamping, and is particularly suitable for being used in a high-low temperature environmental cabinet with compact structure and small space.