Abstract: Diurnal variation in net photosynthetic rate (Pn) of Elaeagnus mollis Diels leaf was measured and the relationships between Pn and the photosynthetic parameters of transpiration rate (Tr), intercellular CO₂ concentration (Ci), stomatal conductance (Gs) and environmental factors analyzed. The results indicate that diurnal variation in Pn exhibits a dual-peak curve ranging between 1.25 ~ 11.35 μmol·m^-2·^s-1. The curve has an obvious midday depression, with the dual peak occurring at 9:00 and 15:00 respectively. Decline in Pn during 11:00 ~ 12:00 is caused by stomatal limitation factor, but by non-stomatal limitation factors during 9:00 ~ 11:00 and 15:00 ~ 19:00. The relationship between Pn and photosynthetic parameters varies with time during the day. 6:00 ~ 9:00 and 15:00 ~ 19:00, Pn exhibits a significantly positive correlation with Tr and Gs, but a significantly negative correlation with Ci. 9:00 ~ 12:00, Pn shows a significantly positive correlation with Ci> and Gs, and a negative correlation with Tr. 12:00 ~ 15:00, Pn is significantly positively correlated with Tr and Gs, while it is positively correlated with Ci. The main environmental factors and their degree of influence on Pn are photosynthetically active radiation (PAR, positive effect) > Ci (negative effect) during 6:00 ~ 9:00; PAR (negative effect) > Ca (atmospheric CO₂ concentration, positive effect) during 9:00 ~ 12:00; relative humidity (RH, positive effect) during 12:00 ~ 15:00; and PAR > Ta (atmospheric temperature, both positive effect) during 15:00 ~ 19: 00.