Non-autoclave aerated concrete was prepared with phosphorous slag with alkali-activator. The porosity and micro-morphology of the aerated concrete pore were analyzed, and XRD, SEM, DSC-TG and FTIR analysis were used to investigate the microstructures and hydration products of non-autoclave aerated concrete. The porosity of the non-autoclave aerated concrete with a bulk density of 500~800 kg/m3 is 66.79%~77.06%. The pore is elliptical and sealed, and the size of most pores is about 0.5~1.5 mm. The major hydration products of the aerated concrete are calcium silicate hydrate gel, gyrolite and hydrated calcium alumino-silicate. The CaCO3 was formed by carbonization of the hydration products.