Abstract: A method of modelling an axial-flow compressor in low speed starting regime from windmilling to idling of an engine is presented. A structural formula for the model is established according to ref. . A method of step-by-step regression is proposed for determining the coefficient matrices of the structural formula. The coefficient functions are determined on the basis of the square, linear and constant terms of the mass flow coefficient respectively in the mathematical model, meanwhile in each portion of the regression the rotor speed is considered to approach zero due to the feature of very low speeds. In result the model represents the performance of the compressor at low speeds very well. Good agreement is obtained between the computational and experimental results.