The paper estimates the influence extent of node voltage sags on general equipment sensitivity by process performance index.Firstly the tolerant deviation of voltage sag is obtained by combination voltage sag characteristics（amplitude and duration） with CBEMA curve

and then Combined with the annual frequency mean and standard deviation of tolerant deviation of voltage sag are calculated and process performance index of node voltage sag is obtained according to mean and standard deviation

which is treated as the index to estimate the influence extent of node voltage sags.The paper takes IEEE-30 as an example

the results of the process performance indices are compared with average severity indices

which proves its effectiveness and practicality.