Abstract: Long-day and shortday photoperiods were set artificially, with natural condition as the control, to examine photosynthetic parameters and chlorophyll fluorescence transient kinetics of 6-year-old ‘Chunjie’ peach cultivar (Prunus persica cv. Chunjie), and to investigate the effects of photoperiod on photosynthesis of the northern deciduous fruit trees. The tree advanced into the dormancy induction period under the shortday condition, and delayed under the longday condition. In the dormancy induction period, the leaf net photosynthetic rate (P_n) and stomatal conductance (g_s) decreased, and the intercellular CO₂ concentration (C_i) increased, suggesting that the P_n decreased because of nonstomatal limitation. Maximum quantum yield for primary photochemistry (φ_Po, or F_v/F_m), potential activity (F_v/F_o), probability that a trapped exciton moved an electron into the electron transport chain beyond Q_A^-(ψ_o) and performance index on absorption basis (PI_ABS) decreased in the dormancy induction period, suggesting that the electron transport capacity of photosynthetic electron transport chain was inhibited, possibly due to the damage to downstream electron transport chain (after Q_A^- acceptor) of PSⅡ reaction center. Longday photoperiod improved P_n in the dormancy induction period, and reduced the range of decline in PI_ABS and the injured degree of photosystem. Shortday photoperiod deepened and accelerated the damage to photosynthetic apparatus significantly. The induced effect of photoperiod was associated with the dormancy processes.