A fast-printable and function-switchable metamaterial based on laser-induced graphene for terahertz (THz) wave modulation in the reflection mode is proposed. The design can modulate the linear polarization of the incoming wave fronts to its cross-polarization from 0.27 THz to 0.41 THz, and linear polarization to circular polarization from 0.48 THz to 0.62 THz. The function of the device can also be switched from a polarization converter to an absorber by bending it with an angle of 57˚. Experimental results showed a good agreement with those of the simulation. The proposed polarization converter may find its application in THz polarization control systems and sensing.