The variation rule of micro-nano structures on titanium alloy surface induced by femtosecond lasers as a function of the laser energy density and pulse number is investigated, and the scanning electron microscope images of these micro-nano structures are shown. The research results indicate that the evolution of micro-nano structure on the titanium alloy surface mainly includes four phases, in the order of no-laser-induced periodic surface structure phase, classical ripple structure phase, classical and non-classical ripple structure coexisting phase, and micro-hump structure phase. Further research indicates that non-classical ripple cycle increases with the increase of laser energy density or pulse number.