Based on the quantitative relationships between rapeseed growth and environmental factors, a simulation model was developed to estimate the shoot dry matter partitioning and yield formation of rapeseed. The dry matter partitioning indices of green leaf, stem and pod varied with the physiological development, and were influenced by the genotype, sowing date, nitrogen level and water status. Green leaf dry matter was regulated by nitrogen nutrition index (NNI). The higher the NNI, the higher the partitioning index of green leaf was. The factor of sowing date was introduced to regulate the partitioning index of pod. A delayed sowing date often induced an increased partitioning index of pod. The validation with different data sets involving variety, sowing date, and nitrogen application rate showed that this model had a good predictability and practicability.