The theoretical and experimental researches on the classical physical picture of magnetic resonance in a rubidium atomic magnetometer under sequential control based on a pulsed pump-probe manner are reported in this paper. The basic principle of this atomic magnetometer is that the light polarization direction will produce rotation related to the magnetic field because of the different absorption and dispersion of the left and right circularly polarized components by the polarized rubidium atoms when the linearly polarized probe beam passes through the vapor cell. A classical physical picture of two-level magnetic resonance is adopted to describe the physical process of interaction between a radio frequency field and atoms, and the specific formula is derived in the rotating coordinate system. Meanwhile, the formula of the output signal acquired by the atomic magnetometer is obtained in the laboratory coordinate system. It is pointed out that the output signals acquired by the rubidium atomic magnetometer are related to the projection of macroscopic magnetization in the direction of the probe beam. The experimental results verify the theoretical analysis. The research results are helpful to deepen the understanding of the classical physical picture of magnetic resonance as well as the basic working principle and parameter setting of atomic magnetometers under sequential control.