This paper presents a mathematical model of a supersonic ramjet.The basic thermoaerodynamical equations of ramjet components are linearized in conformity with small perturbation.Then the transfer functions of the components are deduced on the S domain.With the method of subsystem in series

the dynamical mathematical model of the ramjet with the inlet normal shock position

the parameters along duct and thrust is formulated under the perturbation of upstream Mach number

temperature

pressure and downstream fuel flow rate of the ramjet.A numerieal example of digital imitation of a real ramjet is completed and gives reasonable results.