The invention discloses a fiber material cytotoxicity detecting method. The detecting method comprises the following steps: arranging the fiber with the united length in order to prepare a flaky monomer, and conducting MTT cytotoxicity detection on the flaky monomer by adopting an extraction method or a direct contact method. According to the method, the fiber is prepared into the flaky sample, and then the flaky sample is subjected to MTT cytotoxicity detection, so that the characteristics of simple operation, good reproducibility and convenience for judgment are achieved, and the problem of filament type fiber that as the length-diameter ratio is large and the specific surface area is high, the safety technology assessment of fiber type medical instrument materials and products cannot be well conducted, is solved.