One of the main characteristics of Mercury is its 3:2 spin-orbit resonance. The analytical model proposed here takes into account this phenomenum thanks to the introduction of two resonant variables. Our basic kernel model must be considered as a base for future computations; it does not include any influence of the other planets, the spin axis is parallel to the third axis of inertia, and the body is supposed to be rigid. The planetary aspects and the angle between the spin and the third axis of inertia will be added as perturbations. The results obtained by our simplified model for the angular variables frequencies are coherent with those iven by existing complete numerical models.