Abstract: The nano alumina films on HP40 steel surface were prepared by metal organic chemical vapor deposition (MOCVD) using aluminum tri-sec-butoxide (ATSB) as precursor in nitrogen at atmospheric pressure. The effects of parameters such as deposition temperature on deposition rate of the films had been investigated using optical microscopy, scanning electron microscopy with energy dispersive X-ray spectrometer, X-ray diffraction and atomic force microscopy. The morphology was also observed. The results show that the deposition rate increased from 0.1 mg·cm-2·h-1 to 0.82 mg·cm-2·h-1 when deposition temperature increased from 503 K to 713 K. Dense nano-alumina films with grain size of 10-15 nm could be gained when the deposition temperature was in the range of 593-653 K. The apparent activation energy decreased with the increase of the N2-ATSB vapor mixture flow rate, different mixture flow rates had different reaction orders, and ATSB′s reaction order was 0.7 ± 0.02.