Abstract: Autotoxicity is a major obstacle in continuous cropping under protected cultivation. Previous studies have shown that autotoxicity is a critical factor in chrysanthemum cultivation under continuous cropping. In this paper, autotoxic effects of aquatic extracts from different parts (litters, leaves, stems, roots) and rhizosphere soil of cultivated chrysanthemum “Gaoyataizi” on the photosynthesis of the same species of crop were investigated. The results show that aquatic extracts, especially the extracts of aboveground parts, significantly decrease chlorophyll content, net photosynthetic rate and leaf photosynthetic activity and stomatal conductance. It however, enhances dark respiration rate. The study shows that inhibiting photosynthesis and enhancing dark respiration is one of the mechanisms of autotoxicity in chrysanthemum.