The grating micro-nano structure is fabricated by picosecond lasers on the 304 stainless steel surface. The size of this micro-nano structure and the surface morphology of this processed stainless steel are characterized. The influences of different laser processing parameters on the micro-nano structure are studied. The result shows that the average power has a significant influence on the laser ablation rate and the size of grating micro-nano structure. If the scanning speed increases, the depth of the grating micro-nano structure decreases, while the width remaines unchanged and the laser ablation rate shows an irregular fluctuation. The laser ablation rate decreases if the processing times increase. The better process conditions for fabricating micro-nano structures on the stainless steel surface are as follows: high average power, high scanning speed and low processing times, under which the superhydrophobic surface of stainless steel can be obtained successfully.