Abstract: In order to test and calibrate electric propeller thrust with a resolution of 0.1 μN, a design using two pendulums was propased. By subtracting the signal of the reference pendulum from the signal of measuring pendulum, most common mode noise can be rejected. By adopting capacity-bridge as displacement sensor, force from 0.1 μN to 1 mN and frequency from 10^-3 Hz to 0.016 Hz can be measured to an accuracy of 0.1 μN.