Surface-functionalized graphene oxide (GO) was prepared by reacting GO with polyethyleneimine (PEI) at room temperature. Fourier transform infrared spectroscopy indicates the preparation of PEI-decorated GO (PEI-GO) and dual roles of PEI in preparing PEI-GO. Temperature-sensitive PEI-GO/PNIPAm composite hydrogels with porous structure were prepared by an in situ freezing polymerization method. The composite hydrogels were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy and differential scanning calorimetry. The swelling and deswelling properties, temperature sensitivity and mechanical performance of as-prepared composite hydrogels were also investigated systematically. The rapid swelling and deswelling rates as well as superior mechanical property were achieved by introducing robust PEI-GO sheets into the porous polymer matrix. The maximum tensile strength of composite hydrogel was 34 kPa when the content of PEI-GO was 3.6%, three times larger than that of neat PNIPAm hydrogel.