Based on the conventional polarization-control technology, a novel 3×3 optical switch, consisting of phase spatial light modulator (PSLM), polarizing beam splitter, mirror, and quarter-wave plate, is proposed. This new configuration of the optical switch grants the features of compact in structure, efficient in performance, and insensitive to polarization of signal beam. In addition, the functions of 3×3 optical switch are implemented bi-directionally in free-space. According to the routing state table of polarization-independent 3×3 optical switch, its operational process is analyzed. By modulating PSLMs and controlling the polarization state of signal, the signal routing is realized, and the switching module of 3×3 optical switch can realize arbitrary port output and exchange for any port input beams without routing conflict. The module has the capability of expansion and reconfiguration. Therefore, it is helpful in the design of large-scale switch matrix.