Graphene oxide (GO) was prepared via improved Hummers method, and then the GO was functionalized with phenyl isocyanate. Subsequently, functionalized GO (iGO) and 4，4′-diphenylmethane diisocyanate (MDI) were mixed under sonication in dimethylformamide (DMF) solvent to obtain a homogeneous mixture. The mixtures were reacted with polyoxytertramethylene glycol (PTMG) and 1,4-butanediol (BD) in DMF solvent to prepare the iGO/thermoplastic polyurethane (PU) nanocomposites (called GO-TPU), while neat TPU was synthesized under the same conditions for comparison. Characterizations were carried out by XRD, FT-IR, XPS, Raman spectroscopy, SEM and mechanical properties were tested. The results show that the phenyl isocyanate is successfully grafted onto the surface of GO. The tensile strength and elongation at break of nanocomposites are increased first and then decreased with the increase of iGO. Uniform dispersion of iGO is observed in the PU matrix when the content is less than 1 %(mass fraction). It is found that the most significant improvement of the tensile strength (4.26MP) and elongation at break (500 %) is obtained with iGO at 1% content. When compared with neat TPU, the increase is 127.1% and 27.3%, respectively.