According to an irrigation method based on water usage characteristics and real-time weather condition during different crop growth stages, whether the crops are in a shortage of water in the growth is determined based on an actual soil water content, a water usage amount of the crops during the given growth stage, and a rainfall amount during the next day. If the shortage of water occurs, the actual water usage amount of the crops is calculated, and a water pump can be self-adaptively turned on to water the crops and an administrator is informed when the reservoir has an insufficient water storage, according to the relation between the water storage amount of the reservoir and the actual water usage amount.