Laser shock forming is an effective method for preparation of micro and nano structures on foils by using laser shock wave and the confining effect of die, which has attracted extensive attention in recent 20 years. In most reports on laser shock forming process, there are two issues. The first issue is that the laser spot spans several microstructure features, which causes difference in shock wave over different features. The other issue is that the laser repetition rate used is less than 1000 Hz, which limits the speed of laser shock forming. In this paper, a laser with repetition rate of 40 kHz and spot diameter of 50 μm were employed to form a groove with width of 200 μm and length of 6 mm on an aluminum foil. The fluctuation of the height and crosssection shape of the formed microstructure in the laser scanning range were analyzed. The results showed that the height of the formed microstructure is relatively stable in the whole laser scanning range.There is certain transition in the height of the formed microstructure at the beginning and end of the microstructure, and the transition length of the end stage is much longer than that of the beginning stage. The formed microstructure crosssection can be fitted by circular arc.