Abstract: This is a paper in the field of ceramics and composites. Ultra-lean iron ore was processed, and the ultra-lean iron ore with a good gradation was used as aggregate to prepare a new type of autoclaved aerated concrete block. Furthermore, the effects of different aggregate content, water-cement ratio and autoclave time on the performance and microstructure of autoclaved aerated concrete were studied. The results showed that with the increase of water-cement ratio, lime content, aggregate replacement rate and autoclave time, the compressive strength of concrete showed a trend of first increasing and then decreasing. When the replacement rate of ultra-lean iron ore aggregate was 40%, the amount of fly ash was 10%, the amount of lime was 18%, the amount of cement was 60%, the water-cement ratio was 0.45 and the autoclave time was 5h,the performance of concrete was at its best. At the same time, the incorporation of ultra-lean iron ore had a great impact on the generation of new phases, the concrete itself and the pore structure.