The invention relates to a dry sandbag construction method based on a blow-fill reef sand cofferdam. The method is characterized in that the method comprises the following steps that (1) constructionsurveying and lofting are conducted, and geofabric bag bodies are processed; (2) a foundation trench is excavated; (3) geofabric bag bodies are laid; (4) a cofferdam bag body is constructed, a bottomlayer dry sandbag is filled, a middle layer dry sandbag is filled, and an upper layer dry sandbag is filled; and (5) after a cofferdam body is completed, protective geotechnical cloth is laid, after top layer sandbag water filling compactness is completed, sun-resistant geotechnical cloth is laid in time, and the whole sandbag cofferdam is wrapped. Through the method, the problem of cofferdam blow-fill construction in regions where materials are scarce and transportation cost is high is effectively solved, and the method has the advantages that local materials can be used, construction is convenient, the requirements for the particle size of filling particles are loose, the cofferdam can be formed rapidly, the construction cost is greatly reduced, and the construction progress is accelerated. The exploitativeness and economical efficiency of the method are fully proved through project implementations.