Early rotor faults diagnosis is essential for induction motor life. The reason for which several signal processing diagnosis methods have been proposed. In order to enhance these methods, it is necessary to use a reliable mathematical model of the physical processed signal. Unfortunately, the stator current is usually obtained from an expensive measurement set-up or a complex modelling of the electric motor. The aim of this paper is therefore to use a model of the motor stator current under rotor fault condition. In other words, the searched model must take into account the effects of the fault. Indeed, it has been verified that the effect of a fault is reflected by an amplitude modulation as well as a phase modulation of the stator current corresponding respectively, to a load torque oscillation and an eccentricity in the air-gap. The paper will also investigate the impact of the severity of the rotor fault on these two types of modulation. Finally, a comparison study between both the simulated signal and the experimental signal is carried out to illustrate the merits of the model and its effectiveness.