Nano-starch has many characteristics, such as the small particle size, large specific surface area，nanometric size effects and nano enhancement. In this study, the corn nano-starch was prepared by a double screw extrusion with six cylinders and the morphology, crystalline property and rheological properties of nano-starch were also characterized. The results showed that the D₅₀ particle size of corn nano-starch was reached to 225.8 nm when the dosage of glycerol was 20%, the dosage of glyoxal was 2.0% under the condition of screw speed was 160 r/min and the second to sixth cylinder temperature is 80, 100, 110, 115, 120 ℃, respectively. The structure of nano starch was integrity and its surface is smooth. The glyoxal reacted with the hydroxyl groups of starch to form the acetal compound and a new absorption peak was appeared in the FTIR spectra. Its TG spectra are similar to the original corn starch, and has the similar thermal stability with the corn starch. The XRD peak of nano-starch was weakened compared with the original corn starch and its crystallization area was obviously destroyed. Nano-starch paste is a pseudoplastic fluid with shear thinning properties as the original corn starch, and with the decrease of particle size of the nano starch, the transmittance of its paste increased. The corn nano-starch has broad application prospects in food processing, preservation and packaging due to its unique nano properties.