The invention discloses an online early warning and setting method for an inter-phase distance protection constant value, comprising: fusing the constant value online early warning method and the setting calculation method, immediately releasing the warning information and entering the process of constant value setting calculation when the sensitivity and selectivity problems of the inter-phase distance constant value are found, wherein the process requires no manual intervention, thereby simplifying the steps and processes of setting calculation and improving the corresponding setting speed of the constant value; using the automatically maintained latest grid model and parameter and mode data for calculation with no more necessity for the personnel of the protection department to manuallymaintain the model and parameters of the power grid, thereby avoiding repeated works; and using the branching coefficient/assisting coefficient calculated in the constant value early warning processduring the setting of the inter-phase distance constant value, thereby avoiding invalid and repeated calculations, greatly reducing the amount of calculation, and increasing the calculation speed.