Abstract: The lightweight micro detonation thruster is consisted of a lot of thrust units containing tiny energetic material By using the instantaneous detonation assumption and the tiny charge mass linear approximation, the impulse and the thrust of a micro detonation thrust unit operating in vacuum are theoretically calculated in this paper Based on that, the influences of specific detonation heat, isentropic exponent and length of the nozzle on the impulse and the thrust are studied The results show that increasing the charge mass, the isentropic exponent and the specific detonation heat can enhance the impulse of a thrust unit, and the nozzle length must be 4 times or more of the charge length to achieve the perfect propulsion performance