Abstract: The EPL EXOR 500 N of Germany GABO company was used to determine the dynamic mechanical properties of carbon and glass fiber composites , which can offer a maximal load of 500 N compared to other DMAequipment . All experiment s were carried out in the three-point bending mode , at 25 ℃ and 10 Hz. The effect s ofexperiment parameters , such as preload , dynamic load , fiber type and modulus on dynamic viscoelasticities wereinvestigated. The result s show that the storage modulus increases with the preload , but decreases with the dynamicload , and the fiber type has little influence on the viscoelastic behavior , but the modulus influences it obviously.