The invention discloses a diversion tunnel sequential blocking method for realizing continuous stream of the down stream of a high arch dam in the storage period. The diversion tunnel sequential blocking method comprises the following steps that firstly, a diversion tunnel to be modified and a first lateral hole are selected in the dry season before gate blocking of the diversion tunnel, a lower half hole of the first lateral hole is blocked, the elevation of the bottom of the first lateral hole is heightened, the height of the opening of the first lateral hole is reduced, and the original size of the opening of a second lateral hole is reserved; secondly, the first lateral hole and the second lateral hole are respectively provided with a bulkhead gate, the second lateral hole which is not modified is blocked through the gate before water storage of a reservoir, and water is supplied to the down stream through the opening of an upper half hole of the first lateral hole; thirdly, after the water level of the reservoir meets the requirement that ecological flow can be discharged by a dam body permanent flood discharging hole, the gate of the opening of the upper half hole of the first lateral hole is closed, and the stream is not cut off in the gate closing process. The diversion tunnel sequential blocking method has the advantages of avoiding stream cutoff of the down stream in the gate closing process, simplifying the dam body structure, shortening the work period, increasing electricity generation gains and reducing engineering investment, and can be widely applied to the technical field of water conservancy and hydropower construction diversion.