The invention relates to a water cooling wall on-line failure early warning method, which comprises the following steps: water power calculation, metal wall temperature calculation, stress analysis, fatigue life consumption analysis, creeping life consumption analysis and entire life consumption analysis. The method calculates the parameters of the flow rate of all pipes of a pipe set, inlet and outlet pressure, wall temperature values in a furnace of each section of the pipes along the length, stress change amplitude values, and the like through a flow and heat conduction rule in real time on line. A small amount of measuring points which are distributed in the pipe sections of each radiation area provided with flow and heat conduction representation and the existing furnace outside inlet and outlet measuring points are combined as calculating and checking points, and the calculating and checking points are input into a computer to calculate and process so as to judge whether unsafe factors of unstable water power, overhigh temperature, fatigue creeping destroy, and the like exist or not. A calculating result displays and records relevant data in real time, and is used as a reference for judging whether the wall cooling wall is safely operated or not so as to achieve the optimal operation of equipment, arrange the examination and maintenance management according to the state, and fully implement equipment state overhaul.