In combination with geoelectric model,the present paper gives the curve showing thevariation of calculation error with optimized wave numbers, revealing the existence of an abruptlydropping stable point.This regularity greatly reduces the wave numbers that calculation requires.In addition,studies show that an abruptly-dropping stable Point is also existent on the curveshowals varistion of etror with density parameter of network.The discovery of this regularitycan considerably reduce the time of two-dimensional finite element direct calculation, and makepossible its full application in the inverse problem.