Using the random function theory, taking seismic energy field in the southeastern part of Gansu province to Shanxi-Gansu-Ningxia boundary region as the random function of space and time, the time ＂weight＂ coefficients and the isogram charts of first several typical fields in the region are studied by the method of natural orthogonal function expansion. The result shows that the time coefficient curves upward and downward changes with large amplitude often meaning the moderate-strong earthquake is going up, while the high values of isogram give the region of earthqake hazard.