The invention relates to an on-line comprehensive monitoring method and device for a mixed-flow pump. The on-line comprehensive monitoring method comprises the steps that real-time running state dataof a mixed-flow pump unit and historical running state data are collected, and the different types of evaluation indexes are established; a state recognition model reflecting breakdown states corresponding to the different types of evaluation indexes is constructed according to the historical running state data; the real-time running state data representing all evaluation indexes in a real-time running state data group are input into the corresponding state recognition model, and the corresponding difference coefficient or residual error is calculated; whether the difference coefficient or theresidual error is higher than a set safety prewarning line or not is judged, if the difference coefficient or the residual error is higher than the safety prewarning line, then the corresponding evaluation index of the mixed-flow pump unit is judged to be in the breakdown state, state pre-warning is conducted. According to the on-line comprehensive monitoring method, the state recognition model is constructed according to the historical running state data of the mixed-flow pump, and the real-time running state data of the mixed-flow pump are input into the state recognition model to judge thesafety state of the mixed-flow pump and predict the potential breakdown of mixed-flow pump equipment.