The preparation of cassava cross-linked starch using sodium trimetaphosphate as the cross-linking agent by extrusion was studied.Effects of screwing speed,reaction temperature,moisture content,content of sodium trimetaphosphate and sodium hydroxide on degree of cross-linking were studied.After the optimization operation,the most significant factor for sedimentation volume was the screwing speed,followed by moisture content,barrel temperature,and sodium trimetaphosphate.The optimum technology conditions are:barrel temperature 110 ℃,screwing speed 150 r/min,moisture content 35%,sodium trimetaphosphate content 0.8%,sodium hydroxide content 0.45%.Under this cross-linking condition,the sedimentation volume of cross-linked cassava starch reached to 0.62 mL.