Study on stress intensity factors of surface cracks in round bars under rotary bending is conducted. Superposition FEM is utilized for numerical analysis and virtual crack closure method is used for stress intensity factor (SIF) calculation. Based on case studies on cracks with different aspect ratios and crack depths, an evaluation method is developed for any rotation angle. And then simulation on single crack has been performed automatically. Results are presented and compared with cyclic loading condition. SIF evaluation method is then extended for two coplanar cracks.