Mode transformation algorithm and universal control mechanism for multiple subsystems in metro-access optical network are proposed to realize a multisubsystem-based virtual passive optical network. By combining the characteristics of different multiplexing technologies, a flexible control node (FCN) is constructed. By defining functional modules of operating table and mode transformation in FCN, a universal control mechanism is created and asynchronous unified control of multiple subsystems is achieved. By introducing step-variable knapsack model and tag matrix, mode transformation algorithm of multiple optical network units is designed to realize load balancing between subsystems and improve bandwidth utilization of multiple subsystems network. Finally, simulation results demonstrate the effectiveness of the proposed scheme.