A constrained link routing algorithm is proposed to solve the problem of unconfigured dilated Benes optical switching chips. First, the algorithm groups the optical switches to be configured according to their lateral constraint and subnet connection relationship, and then it optimizes the optical switch combination state to form a link route that satisfies the switching requirement. In this manner, the configuration efficiency of optical switching chips is improved since no processing is required for other idle optical switches. Taking a 16×16 dilated Benes optical switching network as an example, the execution process of the constrained link routing algorithm is described and compared with other configuration routing algorithms. Furthermore, the role of the algorithm in improving the fault tolerance of a chip when its optical switch loses the switching or light-passing function in the chip network is analyzed.