Abstract: Hydroxamated Sodium alginate with efficient flocculant were prepared by the successive heterogeneous esterification and hydroxamation of Sodium alginate under the certain conditions. And through the study on the flocculation performance of diatomite, the SA flocculant dosing quantity was carried out favorably with 2.4mg /L at20℃ for 30min in flocculant, the removal rate was 83.01%. The dosing quantity of the HSA with only 0.8mg /L, the removal rate was 91.53% and the ratio of liquid to solid was 2.33, and it had better characteristic in flocculant.