The invention relates to a nano composite coating and a preparing technology thereof, in particular to a preparing technology for a high-aluminum-content ultra-dense Al-Cr-Si-N nano composite coating. An Al-Cr-Si-N nano composite coating is deposited on a metal or alloy base body through the high-power pulse magnetron sputtering technology. An Al-Cr-Si alloy target is selected as a target material, wherein the atomic ratio of Al to Cr to Si is 6:3:1, purity is 99.8 wt.%, and the size is 300 x 100 x 5 mm; before film coating, inflation of Ar is conducted firstly, striking is conducted at the bias voltage of -800 V, high-power pulse magnetron sputtering of the Al-Cr-Si target is conducted, and bombardment cleaning is conducted on the surface of the base body. Then, the bias voltage is reduced to -30 V, an Al-Cr-Si transition layer is deposited, then inflation of the reaction gas N2 is conducted finally, and deposition of the Al-Cr-Si-N coating is started. The related preparing technology for the high-aluminum-content ultra-dense Al-Cr-Si-N nano composite coating is simple, repeatability is good, and industrial production is easy. The prepared Al-Cr-Si-N coating is high in hardness, good in tenacity, low in internal stress and excellent in abrasion resisting performance; and the coating organization structure is extremely dense and is firmly combined with the base body, and the high-temperature oxidation resisting capability is high.