Abstract: In order to realize the multi-usage on one high power electron irradiation accelerator, the 270° bend branch is needed to be researched. The beam dynamic design and calculation were done for 270° bend branch with the Trace3D code. Two schemes of bend magnet were designed. One is 270° bend and the other is double 135° bend. The design and calculation of the 270° and double 135° bend magnets were done by using two-dimensional and three-dimensional electro-magnetic field calculation code. The calculation result shows that there is a big difference between the simulation and the beam dynamic demand of the field distribution of 270° bend magnet. Because it is very difficult to adjust the field of 270° bend magnet during the commissioning, the double 135° bend magnet is preferred to be used.