Abstract: With upland small forest watershed in Japan as the objective,the relationship between discharge and flood processes of suspended sediment were researched using automatic samplers(ISCO) and water-stage recorder.Resultsshow that the major sources of sediment are forest paths,stream channels and the bare land beside stream channels.The concentration of suspended sediment is well interrelated with that of total sediment.The change of concentration of suspended sediment with the discharge processes follows a clockwise variable lasso.The discharge process of suspended sediment shows a wave-pattern.The maximum concentration of suspended sediment and peak discharge appear almost at the same time,which belong to the synchronic pattern.The discharge amount of suspended sediment is mainly decided by the maximum precipitation in 10 min,each rainfall also greatly contributes to suspended sediment discharge.Suspended sediment discharge from one storm accounts for about 5 % of the total annual sediment discharge.A few storms contribute 30 % of yearly suspended sediment discharge.