Rapeseed acts as an important oil crop in China and breeding for high yield is of great interest. Analyzing agronomic traits of rapeseed germplasm can provide foundational information for selecting excellent parental materials, which will be subjected for making crosses, e.g. to improve important traits in rapeseed. In the present study, 213 breeding lines of B. napus L., which were collected from the main rapeseed production area of the Yangtze River, was used for exploring the relationship between 10 agronomic traits and yield per plant, under the climatic conditions in Chengdu Flat. The statistical analysis including simple correlation analysis, path analysis, multiple regression analysis and principal component analysis, were conducted. The results showed the great divergence on the agronomic traits of rapeseed resources from different regions. The yield per plant was positively correlated to plant height, the effective length of main inflorescence, the number of first effective branch, the number of effective silique on main inflorescence, the length of silique, seeds per silique, and 1000-seed weight, while negatively correlated to the period of vegetative growth. The yield per plant was directly contributed by three factors including plant height, seeds per silique and the number of first effective branches. The indirect effect on plant yield was the effective length of main inflorescence > the number of effective silique on main inflorescence > branch height. By stepwise regression analysis, the yield per plant was mainly determined by plant height, seeds per silique, branch height, and the number of first effective branches. Based on the phenotypic variation using the principal component analysis, these genotypes were grouped into four major categories, consisting of plant height related factors, growth period related factors, yield related factors and plant type related factors. Taken together, the yield per plant in the ecological region of Chengdu Flat was largely contributed by plant height, grain number per pod, primary branch height, and number of primary effective branch. These results would provide a valuable information for selecting elite parental lines in rapeseed breeding.