The twisting response of armchair graphene nanoribbons with tilt grain boundaries is theoretically and numerically investigated. It is found that the critical instability twist rate of graphene nanoribbons with grain boundaries is generally about 10% higher than that of common armchair graphene nanoribbons when the width of nanoribbons is less than 4.0 nm. Our analytical analysis indicates that the strengthening effect is resulted from the rotation of the compressed direction, deflection of grain boundaries, and the reflexing of the creased angle in nanoribbons: the rotation of the compressed direction induced by grain boundaries improves the buckling strength of nanoribbons due to the chirality-dependent buckling in graphene; the deflection of grain boundaries leads to a nonzero strain in the axle wire of nanoribbons, which eventually decreases the compressed stress; grain boundaries induce a spontaneous creased angle in nanoribbons, which is reflexed under twist loading and impedes the propagation of instability in nanoribbons. Furthermore, we found and demonstrated that grain boundaries changed the transport properties of twisted graphene nanoribbons. It is expected that our findings would improve the fundamental understanding of the strain-engineering of graphene nanoribbons used in nanodevices.