Phenotypic plasticity is the ability of organisms to respond to environmental changes. Understanding and leveraging crop phenotypic plasticity is crucial for mitigating the threats caused by climate change. Here, we assessed phenotypic plasticity in multi-environment trials over 4 years, covering a wide geographical area, using 505 inbred lines from a Brassica napus genetic diversity panel. The observed phenotypic variation for seed oil content (SOC) was influenced by three environmental indices (precipitation, diurnal temperature range, and ultraviolet B) during the flowering or pod-filling stage alongside five plasticity genes. Leveraging this information with climate records, we developed a predictive model to estimate SOC for various planting dates in seven major production regions, and validated the accuracy of our predictions in new environments. With the quantified plasticity conferred by genetic variation in the five plasticity genes, we identified an optimal haplotype for each production region for adaptability to future climate projections. This study offers valuable insights and selection of materials to mitigate the adverse effects of climate change on agriculture.