Abstract: Atomic polarizability can influence the sensitivity of atomic magnetometer. As the buffer gas of Cs vapor cell was about 13 332.2 Pa, the two pump light frequencies were locked toF=4F=3 and F=3F=4 of Cs D1 transition respectively, the population dynamics of the magnetic sublevels of ground states and excited states were calculated. We find that with the sustained action of pump light ,the population of F=3 and F=4 are pumping to |F=4,mF=4, and the polarizability reaches maximum value. At the same time the signal-noise ratio of experimental result increases effectively by using two pump beams, then the sensitivity of atomic magnetometer increases by 34%.