Using XRD and SEM analysis, the types and morphology of autoclaved aerated concrete (AAC) hydration products in different water-to-binder ratio (w/b) and different autoclaved system were studied. Strength test shows that, Using w/b=0.25 and autoclaved curing 190°C for 8h, AAC with dry density 765kg/m3 and compressive strength 7.5MPa was made. XRD and SEM analysis indicate that, the higher the autoclaved temperature is, the smaller the size of hydration products (most of them are tobermorite and hydrogamet) is, and the crystallinity has a little increase; with the extension of autoclaved time, the size of products is smaller, the crystallinity is first increased and then decreased, the crystal form of tobermorite turns 1.1nm into 1.4nm; the less the w/b is, the smaller the size of products is, and the higher the crystallinity is, and tobermorite turns 1.1nm into 1.4nm.