The invention discloses an online early warning and setting method for a zero-sequence current protection fixed value. According to the method, an online early warning method and a setting calculationmethod for the fixed value are fused together, when the problems of sensitivity and selectivity of the zero-sequence current fixed value are found, early warning information is issued immediately anda fixed value setting calculation process is carried out, wherein the manual intervention is not needed in the process, so that the steps and the process of setting calculation are simplified, and the corresponding speed of fixed value setting is increased; newest automatically-maintained models and parameters of a power grid and mode data are adopted to carry out calculation, and the personnel at the protection agency do not need to manually maintain the models and the parameters of the power grid, so that the repeated work is avoided; and furthermore, a zero-sequence branch coefficient/zero-sequence sideline current addition coefficient obtained by calculation in the fixed value early warning process is automatically reutilized in a zero-sequence current fixed value setting process, sothat invalid and repeated calculation can be avoided, the calculated amount is greatly reduced, and the calculating speed is increased.