Abstract: The oilseed flax yield formation model was developed to predict biomass yield and provide scientific guidance for oilseed flax production, which was an important sub model of oilseed flax development model, APSIM-Oilseed flax. Its’ accuracy was related to the performance of APSIM-Oilseed flax. In the study, the oilseed flax yield formation model was developed for Northwest China using data generated from experiments, and was calibrated and validated under varying fertilizers, seeding methods, planting densities, nitrogen and phosphorus application conditions. The experiments were conducted at Dingxi and Yuzhong of Gansu Province from 2012 to 2015. Calibration was done using data for 2012–2013 and validation with data for 2014–2015. Two methods, yield component factors method and grain pod ratio method, were used to build oilseed flax yield formation model. The oilseed flax yield formation model of yield component factors was based on genetic parameters, such as, number of pods per unit area, grains number per pod, grain weight and water and fertilizer stress factors. The oilseed flax yield formation model of the grain pod ratio was based on grain pod ratio and total dry matter. The results showed that the average RMSE for the model-simulated and field values related to the yield component factors method under different fertilizers, sowing densities in Dingxi was 133.47 kg per hm². Then it was 195.51 kg per hm² for the grain pod ratio method. Then R² values were 0.819 8 and 0.743 9 for the yield component factors and grain pod ratio, respectively. The average RMSE was 140.70 kg per hm² for the yield component factors method under varying nitrogen and phosphorus levels in Yuzhong and it was 193.22 kg per hm² for the grain pod ratio method. The R² values were 0.832 9 and 0.805 8 of yield component factors and grain pod ratio, respectively. The validation results showed that the yield component factors method was better than the grain pod ratio method in simulating oilseed flax yield formation. In view of different varieties of oilseed flax under varying experimental treatments, the yield component factors method simulated oilseed flax yield with high accuracy and versatility using the number of pods per unit area, seeds number per pod and grain weight as genetic parameters.