In order to analyze the change of flow field in the nozzle, the thrust of the axisymmetric nozzle is calculated using the 1-dimensional calculation model and the 2-dimensional calculation model based on FLUENT, and the difference between the 2 calculation results is analyzed. The effects of pressure, expansion angle, expansion ratio, length of expansion section and viscosity of gas jet on the calculation of nozzle thrust are studied by orthogonal design method. The results show that the thrust difference has a linear relationship with the combustion chamber pressure. The difference of thrust increases with the increase of gas viscosity. When the initial expansion angle is larger and the exit expansion angle is smaller, the difference in thrust is smaller. The difference of thrust decreases first and then increases with the increase of the expansion ratio, the length of the expansion section and the radius of the throat. In the case of low pressure and low viscosity, the 1-dimensional calculation method can be used to calculate the nozzle thrust. Otherwise, the 2-dimensional calculation method is more suitable.