To achieve the thinning and polishing of small-size copper-plated InP wafers using 8-inch chemical mechanical polishing （CMP） equipment， it's essential to enhance equipment compatibility， streamline process steps， and mitigate issues like cracks and surface particles on InP wafers due to excessive handling. Initially， employing custom-made molds allows the processing of small-size InP wafers on 8-inch CMP equipment. Subsequently， to address the brittleness of InP wafers， adjusting the equipment's polishing head pressure， speed， and polishing pad speed， among other process parameters， is crucial to satisfy the demands of the subsequent bonding process. Experimental validation shows that with the use of special molds and the polishing head pressure set to 20.684 kP， along with polishing head and pad speeds of 93 r/min and 87 r/min， respectively， the InP wafer's surface roughness achieves R_a≤1 nm， and the copper layer's removal rate is 3 857×10^-10/min. This preparation ensures defect-free bonding with 8-inch wafers， eliminating voids at the bonding interface. The CMP process for 2-inch InP wafers on 8-inch equipment significantly lowers CMP costs， prevents the increase in surface particle size and scratches during wafer transfer， and facilitates hybrid bonding and Cu interconnections between InP and Si wafers.