In order to meet the high requirements of precision

timeliness and data storage of on-board aero propulsion model

a new method of onboard modeling was proposed. The similarity criterions used in traditional on-board steady-state model were deeply discussed

and a similarity criterion with higher modeling accuracy was obtained. Based on the new similarity criterion

a high precision steady state variable model was established

which includes the nonlinear 2 order term in the Taylor expansion

and the inaccuracy problem of the traditional piece-wise linear method in the condition of large flight envelope and variable state was solved effectively. In order to solve the problem of the prominent difference between engine installed thrust and net thrust under supersonic state

the simplified inlet model considering the outflow characteristics is established

and a method is given to calculate the installed thrust

the part of the installed thrust compatible with the similarity criterion was computed by the above simplified engine model

while the spilled air fluid resistance

the deflation resistance and some part of engine net thrust incompatible with the similarity criterion were calculated by the simplified inlet model. The simulation results show that the error of the on-board propulsion system model based on the new similarity criterion has the advantages of large flight envelope and variable state adaptability

and the error of output parameters are within 0.5%.