A mechanical-pneumatic combined corn precision seed-metering device was designed based on the structure of mechanical inside-filling seed-metering device and the single-seed reserving principle of the pneumatic seed-metering device. The basic structure and the working principle were expounded here. The critical components were designed based on the calculation. It’s performance such as working air pressure, seed overlap index, missing index and seed allocation eligible rates was investigated under laboratory. Experiment results indicated that this device had superior eligible rates of the seed individual spacing, low working air pressure and high speed adoptability.