The invention provides a rapid flood forecasting method and device based on rainfall similarity and model parameter intelligent adaptation, and the method comprises the steps: 1, building a rainfall flood conversion model, and recognizing the rainfall flood features; step 2, calculating the similarity of flood-causing factors: starting from the magnitude of flood-causing rainstorm, the rainfall pattern and the size of each component influencing rainfall in the early stage, calculating a similarity index vector based on a similarity theory, and quantifying the similarity among the flood-causing factors; step 3, transferring parameters, and constructing adaptation mapping among rainfall and flood samples: mutually transferring the parameters among the rainfall and flood samples, creating a model precision matrix after parameter transfer, establishing mapping between similarity index vectors and the precision matrix, and determining the importance degree among similarity indexes; and step 4, intelligent parameter adaptation: based on similarity calculation, clustering analysis and collaborative filtering theories, the reference model uses each set of parameters to forecast the precision of historical similar flood, the parameter with the highest precision is adapted to the model, and flood forecasting is carried out.