The invention discloses a fixing device for a scanning electron microscope test of fibers and a test method. The device comprises an octagonal column body, wherein an octagonal frustum is formed at the upper end of the column body and comprises a top surface and eight inclined surfaces, and multiple fiber samples are fixed on each inclined surface through conductive tapes. The method comprises steps as follows: (i) the device is cleaned; (ii) samples are selected; (iii) the samples are fixed; (iv) the electron microscope test is performed. The device is reasonable in structure, convenient to operate and wide in application range. Sample changing times are effectively reduced, the sample changing time is effectively shortened, when each group of samples are tested, the uniform degree of a sizing agent, the smoothness and residue conditions of surfaces of the fibers can be observed, and whether diameters of different monofilaments of each group of fiber bundles are consistent or not can also be observed.