In order to investigate the failure mechanism, dynamic changing law and the effect of leakage and blockage fault of spacecraft propulsion system, a dynamic simulation of some pressure-fed propulsion system was conducted based on the modular model library previously. The leakage and blockage fault of gas pressurization lines were simulated with the method of Realizable k-ε model and one-dimensional compressible duct model respectively. The leakage and blockage fault simulation for propellant lines were carried out with the finite element state-variable model and variable flow coefficient model respectively. The dynamic simulation of the propulsion system was carried out and some interesting results have been obtained as follows. Firstly, due to the leakage and blockage fault of gas pressurization lines, the pressure boost couldn′t meet the need of operational state, resulting in the propellant inadequacy and pressure drop in propellant lines. Secondly, because of the leakage and blockage fault in propellant lines, the mixture radio would deviate from the designed ones, resulting in the sliding down of the propulsion system performance. Although both of the leakage and blockage fault would make the propulsion system performance slide down, there are differences between the two faults. Firstly, due to the blockage fault, the upstream pressure of faulty component is substandard and less propellant is consumed. Secondly, due to the leakage fault, the upstream pressure of leaking object is lower than normal value and too much propellant is consumed.