Efficient design procedure is introduced for the design of miniaturized contiguous band manifold-coupled multiplexer using the combination of the circuit-full-wave-based optimization in this study. Systematic methodology is based on the design of miniaturized channel filters using circuit model extraction and H-plane manifold network with hybrid optimization. The multiplexer is firstly analyzed in circuit level, and relevant lengths between channel filters and the lengths between each channel filters to manifold junction are determined meticulously to compensate for the channel interaction and mismatching effects of individual channels. Then, full-wave model is constructed and simulated by using corresponding length values. This method has been applied for the design of six-channel contiguous band waveguide multiplexer as an illustration. The obtained results show the efficiency and validity of the proposed method.