In piston pressure measurement, small pressure changes rely on small weights, which cannot achieve continuous change of pressure output, and weights-based pressure measurement also has difficulties in automation. This paper proposes a pressure measurement device using magnetic balance based on opto-mechanical design, to explore the feasibility of the electromagnetic balance method to achieve pressure measurement. In the device, the weight gravity measurement originally used for balance is replaced by an electronic scale, without manual weight addition and subtraction, and the balance force is directly weighed by the scale. Through magnetic repulsion, the spacing in the magnet pair is adjusted to continuously output the required pressure. This method can transform the process of manually placing weights for the balance into the process of real-time continuous force value reading of the scale to finally achieve balance. The experimental analysis demonstrates the influence of the magnet on the reading of the electronic scale. In the pressure output test experiment and analysis, the precise relationship of the distance between the magnets and the magnetic force output is obtained, which proves that the device is effective. It is feasible to replace the small weight in piston manometer with the electromagnetic balance method.