It has been found that the composites of carbon nanotubes (CNTs) and epoxy resin could greatly enhance damping ability while the stiffness is kept high. In this paper, carbon nanotube enhanced epoxy resin is fabricated. A testing apparatus for obtaining composite dynamic properties is set up. In particular, the loss factors are measured. Experimental results show that CNT additive can provide the composite with several times higher damping as compared with pure epoxy. A finite element model is built to simulate the composite damping. CNT diameter and segment length are investigated using the developed model. Results show that composite damping is insensitive to CNT segment length while the effect of CNT diameter on composite damping is significant.