Abstract: Micro-thrust measurement device based on torsion pendulum structure is a common method for micro-thrust measurement of space micro-thruster. Aiming at the calibration problem in micro-thrust measurement, the electromagnetic force constant characteristic based on voice coil motor was studied. The composition and function of the voice coil motor and its calibration application in micro-thrust were introduced. The distribution of magnetic field in voice coil motor and the variation of electromagnetic force under the control factors of coil current, relative distance between coil and magnet were analyzed. An experimental system of constant force characteristics of micro-electromagnetic force was built. Based on the weighing method of high precision electronic balance, the precise electromagnetic force was obtained. With the criterion of electromagnetic force error less than 5%, the stable force output of voice coil motor was obtained, which will lay the foundation for the micro-thrust calibration of torsion pendulum.