The invention discloses a debris flow source starting simulation apparatus based on a combined action of surface flow scouring and rainfall. The debris flow source starting simulation apparatus comprises a water storage box, a rear water gathering apparatus, a rainfall apparatus, a frame-type support, a material box, a flow area, an accumulation area and a waste water collection apparatus, wherein the gradient of the fluid area is fixed by virtue of a rear-mounted frame-type support, the gradient of the material box can be fixed by adjusting the front-mounted frame-type support, and the flow area and the material box are connected by virtue of a hinge and elastic rubber. By virtue of a suspended elastic gridding rope, an accumulation state and characteristics of accumulation bodies can be observed in real time. The rear water gathering apparatus can realize the surface flow scouring by virtue of 7 to 10 bundled water streams and two water flow obstacles. The debris flow source starting simulation apparatus can simulate the starting, moving and accumulation situation of debris flow under the combined action of the surface flow scouring and the rainfall. By changing the gradients of the material box and the flow area, the starting mechanism of the debris flow under different gradients can be researched. By adopting the debris flow source starting simulation apparatus, the starting process of the debris flow under the combined action of the surface flow scouring and the rainfall can be actually simulated.