The invention discloses a sample preparation method for carbon fiber tensile property test, and the sample preparation method is implemented by a sample preparation device. The device comprises a main support, a central shaft, at least two multifilament-winding frames, fixed rods and extensible rods, the central shaft is mounted on the main support, the fixed rods and the extensible rods are used for supporting the multifilament-winding frames, one end of each fixed rod and one end of each extensible rod are fixed with the multifilament-winding frames correspondingly, and the other end of each fixed rod and the other end of each extensible rod are fixed on the central shaft. The sample preparation method includes the steps: firstly, preparing epoxy resin glue solution, then winding a to-be-tested carbon fiber multifilament on the multifilament-winding frames, and subjecting the to-be-tested carbon fiber multifilament to impregnation in the epoxy resin glue solution for 0.5-10min; secondly, placing the carbon fiber multifilament back to the main support after impregnation is finished, adjusting the extensible rods to control the tension of the carbon fiber multifilament subjected to impregnation, and adjusting the carbon fiber multifilament to be flat; and thirdly, drying for 30-120min at the temperature of 60-150 DEG C prior to cooling, and cutting off the cured carbon fiber multifilament to prepare a test sample. By the sample preparation method, sample preparation time can be shortened greatly, the test sample can be flat, uniformity of the sample is guaranteed, and finally accuracy of test results is guaranteed.