The channel evolution under combined action of reservoir and river course sand excavation has its uniqueness.Taking the Lower Reaches of Minjiang river for example, the paper analyzed the channel evolution under combined action of reservoir and channel sand excavation. The results showed that under the combined action of reservoir water discharge and channel sand excavation, the evolution of lower reaches of Minjiang mainly presents longitudinal and lateral large scour, the area of channel cross section increases significantly, and the sediment loss is great. The river bed shows more stable and the changes of scouring and silting is slight in North port while the sand excavation is forbidden. The channel evolution caused by reservoir and river course sand excavation aims to reach balance between scouring and silting. Under combined action of reservoir and channel sand excavation, the evolution presents three characteristics: the channel scour is aggravated and the river bed erosion is in large scale:the fluvial rule is more complicated and the evolution trend is difficult to predict accurately;the adverse effects of channel evolution is very severe.