To improve the signal to noise ratio (SNR) and the short-term stability of cesium atomic fountain clocks,the work of two-laser optical pumping is presented theoretically and experimentally.The short-term stability of the NIM6 fountain clock has been improved by preparing more cold atoms in the |F =4,mF =0> clock state with a shortened cycle time.Two π-polarized laser beams overlapped in the horizontal plane have been applied after launching,one is resonant with|F =4> → |F'=4> transition and the other is resonant with |F =3> → |F'=4> transition.With optical pumping,the population accumulated in the |mF =0> clock state is improved from 11％ to 63％,and the detection signal is increased by a factor of 4.2,the SNR of the clock transition probability and the short-term stability are also improved accordingly.