Abstract: The energy in ecosystems is redundant. Not only the energy within a trophic level is redundant,but the energy flowing among the different levels is redundant. Ecosystems are a redundant system consisted of continuous multi-sources of energy. As soon as energy redundancy in one trophic level is not able to sustain the downward trophic level, the energy flow will stop. Energy redundancy limits the number of trophic levels.At the same time, energy redundancy within the trophic level and between trophic levels maintains normal energy flow and stability of trophic structure in ecosystems. Researches indicated that, in terms of explanation of diminishing energy at trophic levels, the concept of energy redundancy is better than the second low of thermodynamics,for the former is more ecological meaningful.