Abstract: In this study, the single-factor experiment was used to analysis the viscosity change rule of sodium alginate aqueous solution under different conditions of temperature, pH, reaction time. Then the orthogonal experiments were used to optimize the conditions of the preparation of low viscosity sodium alginate. By analysis of variance, the best conditions for preparation of low viscosity sodium alginate was：65℃,pH=2.5,and the reaction time was 8 hours. By spray drying technology, the liquid ultra-low viscosity sodium alginate was made into solid powder.