The discharge research of the residual cryogenic propellant used in the CZ-3A third sub class was studied. The liquid hydrogen and liquid oxygen cryogenic propellant flow inside of the two different discharge pipeline was calculated. The liquid propellant will be vaporized, which attributes to the pressure depression along the pipeline. The gas-solid or the pure gas flow appears at a certain location. According to the each case of the flow, the model and the control equations of pure liquid, gas-liquid, gas-solid and pure gas was used respectively. The results show the pipe 1 is better when the liquid hydrogen is discharged and the pipe 2 is better when the liquid oxygen is discharged. The flow parameter at the pipeline exit through calculation is useful for further study.