The invention discloses a preparation method for low viscosity sodium carboxymethyl cellulose for foodstuff. Under the conditions of proper temperature and stirring, wood pulp cellulose raw materials which are pulverized and pretreated is reacted with ethanol solution of sodium hydroxide in a kneader to form soda cellulose; ethanol solution of monochloroacetic acid is added, and the temperature of the reaction system slowly rises for carrying out etherification reaction; hydrochloric acid solution is dripped to neutralize residual sodium hydroxide in the system, and reaction material is rinsed twice by ethanol and hydrogen peroxide solution; and finally, the sodium carboxymethyl cellulose can be prepared after the steps of drying and pulverization are accomplished. The method has the advantages of simplicity, low cost, high yield and convenient operation, the product is white or yellowish powder, the purity is high and is no less than 99.0 percent, and the viscosity is low and ranges from 22 to 48 Mpa.s; and besides, the sodium carboxymethyl cellulose has favorable homogeneity of substitution and good acid resistance, can be widely applied to foodstuff and beverages to be used as emulsified and suspended stabilizing agent to play the role of thickening, and can improve the mouthfeel of the foodstuff.