To explore the effects of manganese toxicity stress on different rapeseed varieties and the mechanisms of manganese tolerance in rapeseed under acidic soil conditions，41 varieties of Brassica napus were used to analyze their phenotypes under normal manganese and manganese toxicity conditions with nutrient solution （300 μmol/L MnCl₂） cultivation to study the effects of manganese toxicity in acidic soil on different varieties of B. napus and the mechanisms of manganese toxicity tolerance in B. napus.The ratio of total fresh mass under manganese toxicity treatment to total fresh mass under normal treatment was calculated.The manganese toxin tolerant variety 427 （Mn-T 427） and the manganese toxin sensitive variety 907 （Mn-S 907） were identified.The physiological mechanism of manganese tolerance in B. napus was preliminarily analyzed.The results showed that manganese toxicity stress significantly inhibited the growth of Mn-S 907，resulting in a significant decrease in shroot fresh weight and photosynthetic rate，severe degradation of chlorophyll，and inhibition of root growth.The excessive accumulation of reactive oxygen species （ROS） in the roots of Mn-S 907 indicated a low clearance efficiency of their antioxidant system.In contrast，Mn-T 427 had significant advantages including less limitation of biomass and the ability to optimize root architecture by increasing root length and surface area to adapt to manganese toxicity stress.The loss of chlorophyll was smaller，photosynthesis was less affected by manganese toxicity，and it had stronger antioxidant capacity.Compared with Mn-S 907，Mn-T 427 alleviates the damage caused by manganese toxicity through regulating root growth，maintaining photosynthesis，and enhancing antioxidant systems.It will provide important germplasm resources and a theoretical foundation for breeding B. napus with high yield in acidic soils.