The spatial channel network (SCN) is a new optical network architecture that can support traffic requests from 100 Gb/s to 10 Tb/s and beyond. Software-defined networking (SDN) has superb management and control capabilities, making it easier to obtain network topology and link load information with it than with traditional networks. Combining the advantages of both, we propose a multi-plane SDN-based spatial channel network (SD-SCN) architecture and focus on solving the routing, modulation format, spatial lane, and spectrum block assignment (RMSSA) problem in static SD-SCNs. In this paper, we build a multi-plane network model of an SD-SCN, design the functional modules of each plane, and give the operation principle of the model. Furthermore, we formulate the RMSSA problem in the static SD-SCN model and propose a heuristic spatial lane and spectrum block minimization and load balancing (MLB2) algorithm to solve the problem. Also, we design an improved ant colony optimization (IACO) algorithm (the heuristic function and iteration criterion are optimized) to implement the routing path assignment function of the MLB2 algorithm. The simulation results show that the MLB2 algorithm can carry traffic requests with minimum network resources, and when the total traffic rate is high, the link load can be balanced by invoking the IACO algorithm to increase the network throughput. The MLB2 algorithm performs better in small-scale networks than in large-scale networks.