The invention relates to an overhead transmission line maximum temperature forecasting method based on an echo state network and belongs to the field of relay protection on power system transmission lines. The method comprises the steps of forecasting the maximum temperature difference deltaTmax(n) along the transmission line based on the echo state network, forecasting the temperature rise variation A (n) based on the echo state network, forecasting the temperature rise variation B (n) based on the echo state network, forecasting the local conductor temperature Tlocal(n) of a transformer substation by virtue of iteration according to the A (n) and the B (n) in combination with the environmental temperature data Ta acquired at the current moment, and adding the forecasted maximum temperature difference deltaTmax(n) along the line and the forecasted local conductor temperature Tlocal(n) to obtain the forecasted maximum temperature difference Tmax(n) along the line. According to the overhead transmission line maximum temperature forecasting method based on the echo state network, the potential current-carrying capability of the line is excavated as much as possible, the conductor temperature is pre-evaluated and the protection action time is adjusted adaptively, and therefore, more time is gained for scheduling and for the emergency control system to take measures to eliminate overload.