The invention provides a network degradation diagnosis method, which comprises a flow degradation calculation method, and the flow degradation calculation method comprises the following steps: obtaining network flow index data under different influence factors, and carrying out normalization processing on the network flow index data of each cell; wherein the network flow index data are a flow service model data size and a current flow data size; and calculating the ratio of the traffic service model data volume of each cell to the current traffic data volume, i.e., the traffic data ratio, andaccording to the cells with the traffic data ratios being ranked from large to small and the larger the traffic data ratio is, the larger the network degradation degree is, so that the method is a method capable of effectively detecting and judging the invisible fault of the network.