Using sodium silicate, anhydrous calcium chloride, aluminum sulfate and sodium Carboxymethyl cellulose as raw materials, polyaluminum calcium silicate cellulose composite (PSiAlCa-CMC) flocculant was prepared under the optimum conditions, and then used to treat the simulated Songhua River water sample. The flocculant was added to the simulated Songhua River water sample to explore the effect of application conditions on flocculation efficiency. The results show that when the dosage is 2.0 mL/L, the flocculation time is 20 min, the stirring speed is 100~140 rpm, the temperature of water sample is 15~20 ℃, pH is 5~6, the PSiAlCa-CMC flocculant has the best flocculation effect. The flocculation effect of cellulose compound flocculant on simulated Songhua River water sample is good, the chromaticity is above 98% and the turbidity is over 92%. The results show that the flocculant successfully flocculates impurities in water and can be applied to sewage treatment in practice.