Disclosed is a method for preparing a micro-nano composite structure through nanosecond laser induced cracks. Firstly, commercial pure titanium TA1 is subjected to surface polishing; then a light path is built and comprises a nanosecond laser device; output light of the nanosecond laser device passes through a reflecting mirror to make the light path turn by 90 degrees; reflected light sequentially passes through a small hole diaphragm, a beam splitter prism, a shutter and a focusing lens to vertically irradiate on a processing station of a movable objective table; the nanosecond laser device, the shutter and the movable objective table are connected with a computer; output laser parameters of the nanosecond laser device are adjusted through the computer; and the polished commercial pure titanium is fixed to the processing station of the movable objective table and subjected to nanosecond laser irradiation, the movable objective table is controlled through the computer to move in the horizontal direction, and the surface composite structure with a micron-structure below 5 [mu]m and a nano-structure below 1 [mu]m combined is obtained. According to the method for preparing the micro-nano composite structure through the nanosecond laser induced cracks, characteristics of crack generation under the heating action of a titanium material and microstructural controllable laser propagation are utilized, the operation is simple, and the processing efficiency is high.