The invention relates to ASA (
acrylonitrile styrene acrylate) 
powder and a preparation method thereof. The preparation method comprises the following steps: adding de-ionized water, an expanding agent, an emulsifying agent, 
acrylate monomers, a cross-linking agent and an initiating agent into a reaction container, and reacting to obtain 
acrylate seed latex; adding the acrylate monomers into the acrylate seed latex, and reacting to obtain core-layer latex; adding 
styrene and 
acrylonitrile into the core-layer latex, and compatibilizing and 
grafting the monomers to the core-layer latex to obtain primary graft 
polymerization emulsion; mixing the rest of 
styrene, 
acrylonitrile, the emulsifying agent and the de-ionized water, and emulsifying to obtain stable 
emulsion; dropwise adding the 
emulsion to the primary graft 
polymerization emulsion containing the initiating agent for reaction, heating for curing to finish a secondary graft 
polymerization process, adding a compound 
antioxidant into the polymerization emulsion, and condensing, dehydrating and 
drying to obtain the ASA 
powder. According to the preparation method, the 
reaction speed and the particle size can be satisfactorily controlled, the 
dyeing property and the 
impact resistance of a product are improved, and the problem of product defects caused by non-tight coverage of a core layer is avoided.