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The plate non-parallelism error of capacitance displacement sensor is studied to improve the thrust measurement accuracy of space-borne micro-thrusters. The relation between the plate nonparallelism error and variable torsional angle is analyzed by taking a typical torsion balance for example. Based on the property of that the plate non-parallelism error and width cosine error are all independent of the direction of torsional angle, a calibration method is presented, and an experimental instrument is designed. A sensor with range of 1mm and effective radius of 3.5mm is calibrated with an increment of 0.5°, and the deviation between the non-parallelism error and its theoretical value is 17.4%. The calibrated results show that the measured thrust error derived from non-parallelism error is rapidly increased to 3.25% when the steady-state torsional angle gets close to the maximum negative angle; and it is gradually increased to 0.04%, corresponding to the measured thrust error of 0.1 μN, when the steady-statetorsional angle gets close to the maximum positive angle; the effective radius of plate is not more than 7mm when the measured thrust error is less than the order of magnitude of μN. [ABSTRACT FROM AUTHOR]