Graphene oxide/polyurethane (GO/PU) composites with significant reinforcement and thermal healable property were developed via in situ polymerization based on Diels-Alder (DA) chemistry for the first time. The PU prepolymer was prepared with GO and blocked by furfuryl alcohol firstly. Then the prepolymer was cross-linked by bifunctional maleimide via DA chemistry. SEM shows that the GO was dispersed uniformly in the PU matrix. The DA and retro-DA reactions were characterized by Fourier transform infrared spectra and differential scanning calorimetry separately. Tensile tests showed that with the incorporation of 0.1 wt% of GO, the tensile modulus of GO/ PU composites increased from 9.80 MPa to 21.95 MPa, and the tensile strength and elongation at break of the GO/PU composites increased by more than 367% and 210%, respectively. Furthermore, the composites possessed thermal healable ability which was inspected by atomic force microscope and strain-stress test with the healing efficiency of 78% determined by recovery of breaking stress in average and the healing mechanism was tentatively proposed.