We investigate theoretically the intense terahertz field-driven electron-transport through a nonmagnetic semiconductor-heterostructure with spin-orbit coupling. It is found that the frequency-dependent conductivity spectra possess splitting resonance-peaks of asymmetric Fano-type, and multiple-photon-process arises with the increasing amplitude of oscillating field. By changing the external field parameters, the purpose of spin filtering may be realized, and 100% pure spin-polarized current at the frequency of Fano-resonance can also be achieved. These interesting features may be a very useful basis for devising a wide range tunable spin filter and realizing pure spin current.