In order to enhance the strength of polyacrylamide（PAM）gel，nanocrystalline cellulose（NCC）was used to prepare AM/NCC composite hydrogel. The effects of NCC on the tensile property，compressive property，adhesion property and viscoelastic property of composite hydrogel were investigated by using texture analyzer and rheometer，and then the microstructure of composite hydrogel was observed by scanning electron microscope （SEM）. The results showed that the tensile strength， compressive stress，adhesive force，elasticity modulus and viscosity modulus of composite hydrogel were significantly higher than those without NCC. When the mass ratio of AM to NCC was 5∶3，the tensile strength，compressive stress and elasticity modulus of composite hydrogel reached the maximum. The toughness of composite hydrogel was significantly enhanced. Meanwhile，the tensile stress and adhesion force were nearly 3 times higher than those of PAM gel. Compared with PAM gel，the network structure of PAM/NCC composite hydrogel became denser. Furthermore，the mechanical strength and adhesion to wellbore wall became better. PAM/NCC composite hydrogel could be used for underbalanced drilling in oil and gas fields.