Modified bagasse retarder (MBR) was prepared by sodium chlorite pretreatment and acid hydrolysis of bagasse in the presence of a catalytic amount of phosphotungstic acid, and its functional groups were analyzed by FT-IR, the influence of hydration heat, XRD and SEM on cement hydration was analyzed, and the retarding effect was compared with that of sodium gluconate (SG) at 20 °C and 50 °C, respectively, MBR contains hydroxyl group, carboxyl group and phosphate group, which has good adaptability to cement, better retarding performance than SG and does not affect the later strength of concrete, which can delay the induction period and reduce the hydration rate in accelerating period.