Photosynthetic process should include both the process of light energy utilization and the process of light energy dissipation. In the latter process, besides the biochemical mechanisms of photorespiration and Mehler reaction,there are also some biophysical processes. These processes can be summarized into follwing three aspects: (1) Energy dissipation through electric cycle around PSⅡ. This cycle includes PS Ⅱreaction center, plastoquinone, and cytochrome b-559. This mechanism can recombine with the charge separated PSⅡ center, so that prevent the oxidation of chlorophyll induced by the longer existence of oxidative P680⁺.(2)Heat dissipation correlated with the thylakoid membrane energization and xanthophyll cycle. This mechanism exists in LHCⅡ，and responses quickly at relatively lower excess light stress (3) Heat dissipation via photosystem Ⅱ hetero-geneity and the turnover of D1 protein. This mechanism bases on the hypothesis that there are two kinds of photosystem Ⅱ.One is photosyn-thetic active with higher linear electron transport and higher fluorescence emission but lower heat dissipation. The other is photosynthetic inactive with lower linear electron transport, lower fluo-rescence' emission and higher heat dissipation. The latter is called dissipative PSⅡ .This dissipative PSⅡ can be reactive directly without protein synthesis or indirectly through D1 protein turnover process.