A polishing device for an indium phosphide substrate and a polishing process are provided, which belong to the technical field of polishing of indium phosphide. The polishing device includes an electrolyzer, and further includes an anode disc supporting rod positioned at a center position of a bottom of the electrolyzer by virtue of an anode lifting mechanism; an anode disc hinged to an upper end of the anode disc supporting rod; a cathode disc supporting rod positioned above the anode disc by virtue of a cathode lifting mechanism; a cathode disc arranged at a lower end of the cathode disc supporting rod; a graphite electrode plate arranged on the anode disc by virtue of a connection mechanism; a group of planet gears arranged on an upper end surface of the graphite electrode plate by virtue of an intermediate driving mechanism; an anode rotation driving mechanism connected to the intermediate driving mechanism; a cathode rotation driving mechanism connected to the cathode disc supporting rod; and a polishing direct current (DC) power supply respectively connected to contacts of the anode disc supporting rod and the cathode disc supporting rod by virtue of wires. By improving the structure of the device and the manufacturing process, a requirement for the environment in the polishing process of indium phosphide is greatly reduced, and electrochemical and mechanical dual-polishing is achieved.