An irrigation method for coastal regions. The method includes: selecting coastal region and collecting natural and environmental data of the coastal region; building a basic database of the coastal region based on high-precision map of the coastal region; establishing a water demand calculation model for coastal crops and a multi-source water supply model, where the multi-source water supply model includes a multi-source water of mixed salt-fresh water calculation model and a freshwater source calculation model; calculating water demand Qdemand during a forecast period according to the water demand calculation model for coastal crops; clarifying salt content Slimit of the water demand during the forecast period; calculating the water supply amount Qsupply in the coastal region during the forecast period according to the multi-source water of mixed salt-fresh water calculation model; and comparing the Qdemand and the Qsupply to accordingly regulate irrigation operation.