The starting process of slumping congeries is the key of Landslide fluidization. Taking Jinlong gully of Yalong River as a typical instance, the characteristics of slumping congeries on the response of heavy rainfall are analyzed firstly, then dynamic mechanism is made to retrieve the starting of slumping congeries by mechanical model. Finally Conclusions of slumping congeries starting response to rainfall are given: (1) The response to rainfall amount is reflected in the transition period of the dry season to rainy season when transformation of debris flows are concentrative happened. (2) The response to rainfall intensity is characterized by short-term index of rainfall intensity, and after calculating the index of rainfall intensity in Jinlong gully, debris flow is likely to outbreak when the index is greater than 800. (3) Taking a loose debris body as the simplified mechanics model, the starting process of slumping congeries is that under the heavy rainfall the increased water force and decreased soil cohesions reduce the stability and then lead to the starting of the slumping congeries and generate debris flow. All the conclusions and results in the paper can provide references for the theory study of landslide fluidization and the starting of debris flow.