The high-temperature oxidation resistance of new austenitic stainless steel NH4 in air over the temperature range of 700℃～1000℃ was studied by using the way of gain weight. The surface morphology、constituent and micro-structure of the oxidation scale was analyzed by using XRD、SEM and EDX techniques. Experimental result indicated that the average oxidation speed of NH4 were 0.064 g/(m2 h)(700℃),0.083 g/(m2 h)(900℃)and0.2786 g/(m2 h)(1000℃).The compositions of oxide included outer Cr2O3 film and inner SiO2 film at 700℃ and 900℃. While at 1000℃ the oxide layer was a mixture of Cr2O3、SiO2 and Al2O3. At high temperature SiO2 layer was formed before Cr2O3 layer, and SiO2 layer was in favor of the formation of Cr2O3 layer.