Based on the reviewing of the current research state of energy input and output at small watersheds in loess plateau region and the study conditions abroad and in home, the basic conditions in nature and input-output of energy in the study area were analysed, from this the study procedure for energy flow analysis was set.which includes scope determination, subsystem division and survey energy calculation, indices analysis and energy flow figure.Taking Huangjia Ercha watershed as a research subject.the capital structure of small watershed system was established and the calculating method for energy flow was made.