Abstract: Acicular calcium carbonate has been widely used as a kind of new inorganic filler of high quality and low cost in the fields of plastics，rubber，paper，and so on.In order to achieve the purpose of simplifying the experimental process and saving resources，this experiment chose an appropriate modifier to synthesize and modify nano-sized acicular active calcium carbonate by ultrasound-assisted one-step method.Various reaction conditions，such as the concentration of solutions，dosage of modifier，reaction temperature，and water content，were considered，and the optimum reaction conditions were obtained by orthogonal experiments：the concentration of solution was 0.05 mol/L，the reaction temperature was 60 ℃，the dosage of modifier was 1.25%（mass fraction），the water content was 60 mL，the ultrasonic power was 250 W，and the stirring speed was 200 r/min.Nano-sized acicular active calcium carbonate was prepared under those conditions and the verification test showed the product′s average particle size was 150 nm，the aspect ratio was 21.7，the activation degree was 98.67%，and the oil absorption value was 0.455 g/g.

Key words: nano-sized calcium carbonate；acicular shape；ultrasound, modification