Limited attention has been given to the persistent impacts of diverse herbicides present in soil on the growth of successive crops in agricultural production. Therefore, the objective of this experiment is to thoroughly examine atrazine residues toxic reactions in lucern (Medicago sativa L.). This experiment aims to thoroughly investigate the toxic response of atrazine in lucern. Lucern sourced from Henan Seed Company in China. The study employed the soil addition method to investigate the impacts and correlations of diverse concentrations of atrazine herbicide residues with growth indicators, photosynthetic features, chlorophyll fluorescence parameters of lucern. The results showed that with the increase of atrazine residue (0.0-2.0 mg·kg-1), the plant height (PH), root length (RL), stem dry weight (SDW) and root dry weight (RDW) decreased to 81.8%, 81.7%, 92.3% and 85.2%, respectively. SPAD value, net photosynthetic rate (Pn), stomatal conductance (GS), transpiration rate (Tr), the PSII maximum quantum yield (Fv/Fo), maximum photochemical efficiency (Fv/Fm), actual photosynthetic efficiency (Y(Ⅱ)), PSII coefficient of photochemical fluorescence quenching (qP) and photosynthetic electron transport rate (ETR) decrease by 62.1%, 83.4%, 84.1%, 95.7%, 76.8%, 11.8%, 84.5%, 46.1% and 63.1%, respectively. However, the intercellular carbon dioxide concentration (Ci) and non-photochemical quenching coefficient (NPQ) increased by 46.2% and 37.5%, respectively. Ci was positively correlated with Fv/Fo, Fv/Fm, qP, Y(II) and ETR (P<0.01), SPAD, Pn and Gs were significantly negatively correlated with Tr (P<0.01), were significantly positively correlated with Tr, Fv/Fo, Fv/Fm, qP, Y(II) and ETR (P<0.01). The potential toxicity risk of atrazine residues to plants was assessed by photosynthetic characteristics and chlorophyll fluorescence parameters. Although herbicide application is essential for food production, appropriate concentration management methods must be adopted to ensure the sustainable development of agricultural ecology.