Toshiko gully on the right bank of Dadu River is characterized by medium and high frequency debris flows,where several severe debris flow disasters occurred.Based on the history of disasters and development characteristics of the gully,formation conditions and development history of debris flow in the gully areanalyzed through detailed field geological engineering investigation,geological mapping for remained mudmarks in typical profiles,particle analysis and volume weight test.Combined with the development characteristics of the Dadu River terraces and glacial melting periods,phases of debris flow in the periods are analyzed and the prediction and assessment of debris flow are made.The research reveals that the formation ofdebris flow has a close relation with ice evolution. Using the historical analysis method,the conclusion canbe draw that Toshiko valley is in a decline phase and the scale of debris flow will be reduced successively.