Mode division multiplexing technology can augment the single-wavelength capacity via orthogonal eigenmodes within a multi-mode optical waveguide. In order to achieve the low-loss, small-size, multi-channel mode multiplexers, an 8-channel mode-polarization multiplexer consisting of digital structures and waveguide structures is designed, fabricated, and measured to improves the integration and transmission capacity of optical interconnects. The digital structures optimized by a novel adaptive direct binary search (ADBS) algorithm works for the TE₀, TE₁, TE₂, and TE₃ modes. The ADBS algorithm can adaptively escape local convergences and greatly reduce time costs because of the introductions of the pooling operator and mutation operator. The waveguide structures designed by the cascaded asymmetrical directional couplers (ADCs) works for the TM₁, TM₂, TM₃, and TM₄ modes. The ADC structures further expands the number of channels based on the digital structure through a cascade strategy. To the best of our knowledge, the digital-waveguide structure with an effective length of about 100 μm is the smallest 8-channel mode-polarization multiplexer. The device is fabricated on a SOI wafer with a 220 nm-thick top silicon layer and a 1 μm-thick silica cladding. The measured insertion loss (IL) and crosstalk (CT) are less than 1.2 dB and lower than -12.5 dB at 1550 nm, respectively. At the same time, the measured ILs and CTs are less than 1.7 dB and lower than -9.3 dB from 1540 nm to 1560 nm, respectively. In addition, clear and open eye diagrams are obtained during the transmission of 256 Gbps signals, verifying the stable and high-speed data transmission capability.