To evaluate the effect of irrigation (irrigation disruption at beginning of flowering, end of flowering, grain filling and control) and biological phosphorus (0, 50, 100 and 150 g/ha) on the yield of Brassica napus L. cv. ‘Hyola 401’, a split plot experiment was carried out based on randomized complete block design with four replications in 2010. The maximum (4.55 g) and minimum (3.25 g) 1000 seed weight belonged to irrigation disruption at the beginning of flowering with 150 and 50 g/ha of biological phosphorus application, respectively. The highest yield of seed (777.58 kg/ha) was obtained from irrigation disruption at the end of flowering with 50 g/ha biological phosphorus, and the lowest yield of seed (120.87 kg/ha) was obtained from irrigation disruption at the beginning of flowering without biological phosphorus. The maximum number of complete pods (17.38) was observed in 150 g/ha of biological phosphorus application by normal irrigation, and the lowest number of complete pods (5.49) belonged to no phosphorus application with irrigation disruption at the beginning of flowering stage. The highest percent of infertile pods (55.29%) was obtained from no phosphorus application with irrigation disruption at the beginning of flowering. And the lowest infertile pod percent (20.67%) belonged to 150 g/ha biological phosphorus application at normal irrigation.