The invention provides an intercepted cofferdam weir reservoir siltation measuring method suitable for sediment-laden rivers. The intercepted cofferdam weir reservoir siltation measuring method includes the following steps: step 1. data extraction: extracting historical sediment measurement data of a river channel at a dam site of a project and relevant river hydrology and diversion system data; step 2. sediment-laden river classification and judgment: carrying out classification and judgment of the sediment-laden rivers according to the sediment median particle size parameters and sediment types in the historical sediment measurement data obtained in the step 1; and step 3. sedimentation calculation of a diversion weir reservoir: step 3-1. determining the sediment input amount of the diversion weir reservoir according to the river annual sediment yield and related parameters; step 3-2. selecting an appropriate method to calculate the sediment output amount of a diversion system according to the sediment-laden river classification determined in the step 2; and step 3-3. working out the amount of sediment deposition in the diversion system through the sediment input and output amounts of the diversion weir reservoir. The method is suitable for most sediment-laden rivers and can provide important support for the design and decision making of construction diversion schemes.