Surface morphology is a critical factor to determine the surface functionality. Ultrafast pulsed laser is a powerful tool to induce multi-scale surface structures on different materials, and thus control their functionalities. This paper presents an experimental study on the micro/nano-scale surface structure formation by femtosecond laser irradiation on stainless steel. The effects of laser fluence, effective pulse number per spot, and repetition rate on the structure morphology and dimension are studied. By controlling the laser parameters, four different types of structures are obtained: (1) laser-induced periodic surface structrues (LIPSS), (2) microgrooves covered by LIPSS, (3) microgrooves/micro-holes covered by LIPSS, and (4) irregular microstructures. The formation dynamics and mechanisms of different structures are investigated.