Abstract: Thylakoid lumen acidification induces high energy state quenching. The xanthophyll cycle-dependent excitation energy dissipation is regulated by thylakoid lumen acidification. Reversely,xanthophyll cycle can protect the thylakoid lumen against over-acidification. Over-acidification in thylakoid lumen induces instability of some luminal components, brings destructive effects on the photosynthetic apparatus, restricts normal turnover of the proteins, and induces photoinactivation of the PSⅡ reaction centers.