Target recognition methods based on feature extraction of bistatic radar polarimetric characteristics face the challenge of feature variation caused by independent rotation of transmit and receive polarization bases. Based on Huynen decomposition and Cameron decomposition theories, this paper rigorously derives ten types of bistatic polarization roll-invariants covering scattering intensity, polarization modulation capability, scattering mechanism, symmetry and reciprocity. Simulations are systematically carried out on dihedral, sphere and trihedral structures, followed by anechoic chamber experimental verification using a self-built bistatic full-polarimetric electromagnetic scattering measurement system. Simulation and experimental results demonstrate that all proposed invariants strictly satisfy roll-invariance under independent rotation of transmit and receive polarization bases. Polarization roll-invariants of different structures exhibit distinct variation laws with bistatic angles, which can provide robust and reliable feature support for bistatic polarimetric radar target recognition.