The invention discloses a northern reservoir spring runoff water source analysis method. The method comprises the following steps of: determining the runoff water source by analyzing the change rule of the daily-scale runoff curve of the spring reservoir in the previous year; dividing the daily-scale runoff into surface runoff and underground runoff, calculating a base flow ratio, determining thestart-stop date of each runoff water source over the years according to the base flow ratio curve, drawing a box diagram of the start-stop date of each runoff water source, and describing the law of the start-stop date of the reservoir spring runoff water source based on the statistical characteristic values obtained by the box diagrams. The method can provide a basis for constructing a reliable and suitable spring runoff forecasting model, and can also be directly used for roughly forecasting the start-end date of each runoff water source in the spring of the next year.