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To identify herbaceous peony cultivars with strong photosynthetic productivity, we compared the photosynthetic characteristics of 20 herbaceous peony cultivars based on four photosynthetic characteristics parameters and established light–response curves under a light intensity gradient, using CIRAS-3 portable photosynthetic dynamic monitoring. The net photosynthetic rate (Pn) showed a “unimodal” diurnal variation pattern, with a peak around 12:00. The diurnal pattern of the transpiration rate was the same as that of Pn. Stomatal conductance values (Gs) showed similar patterns among the cultivars, with only small differences. The daily variation in intracellular CO₂ concentration (Ci) showed an opposite trend to that of Pn. When the photosynthetically active radiation was 0–400 μmol·m⁻²s⁻¹, Pn increased linearly and gradually with increasing light intensity. ‘Xueyuanhonghua’, ‘Qingwen’, ‘Taohuafeixue’, ‘Chifen’, and ‘Qihualushuang’ showed high photosynthetic productivity. ‘Xueyuanhonghua’, ‘Fushi’, ‘Qingwen’, ‘Tianshanhongxing’, ‘Qingtianlan’, ‘Dafugui’, and ‘Hongfushi’ had high light saturation points and the highest light resistance. ‘Xueyuanhonghua’, ‘Qingwen’, ‘Taohuafeixue’, ‘Tianshanhongxing’, ‘Qingtianlan’, ‘Guifeichacui’, ‘Chifen’, and ‘Hongxiuqiu’ had low light compensation points. Thus, two cultivars with strong photosynthetic productivity, ‘Xueyuanhonghua’ and ‘Qingwen’, can be cross-bred to obtain both light- and shade-tolerant plants. This study provides a theoretical basis for breeding new cultivars with high photosynthetic productivity.