Abstract: In the past several years, the miniaturization of Liquid Rocket Propulsion Systems advanced tremendously. The advanced micropropulsion systems are characterized by the miniaturization, high pressure and fast response. For these micropropulsion systems, the mathematical models of components are derived and gathered together. For the divert thruster of micropropulsion system, the variation of the combustion chamber pressure during impulse working and the pressure variation during closing the divert valve are investigated and analysed. It provides a basis for research of the dynamic response of the whole micropropulsion system.