To clarify the runoff characteristics of sheet erosion during maize growing season, change characteristics of runoff and hydrodynamic parameters of sheet erosion processes were studied on cross ridge sloping farmland with different slope gradients during whole maize growing stage in purple soil area based on the combining method of micro-plot and artificial simulated rainfall. The results showed that: (1) The time of sheet erosion occurrence was after 8 minutes of the rainfall on slope gradient with 15°at the jointing stage and tasseling stage, and the time of sheet erosion occurrence had the significant difference between the jointing stage, tasseling stage and seedling stage, mature stage. The time of sheet erosion occurrence was after 6 minutes of the rainfall on slope gradient with 20°at the jointing stage and tasseling stage, and the time of sheet erosion occurrence had the significant difference between the jointing stage, tasseling stage and seedling stage, mature stage. (2) On slope gradient with 15°, the runoff amount and runoff rate showed that mature stage＞seedling stage＞tasseling stage＞jointing stage, and the runoff amount and runoff rate was 31.25 L and 1.04 L/min respectively at the mature stage. However, on slope gradient with 20°, the runoff amount and runoff rate showed that seedling stage＞mature stage＞tasseling stage＞jointing stage, and the runoff amount and runoff rate was 34.62 L and 1.44 L/min respectively at the seedling stage. The runoff amount ascended with the increasing slope gradient during whole maize growing stage. (3) On slope gradient with 15°, runoff shear stress had no significant difference among the growing stages of maize, and the other hydrodynamic parameters showed the minimum at tasseling stage. On slope gradient with 20°, unit stream power had no significant difference among the growing stages of maize, and the other hydrodynamic parameters showed the minimum at tasseling stage or jointing stage. Stream power and section flow energy were the best parameters closely related to the runoff rate of sheet erosion process on cross ridge sloping farmland. Runoff characteristics of the cross ridge sloping farmland could be well described by stream power and section flow energy on the condition of our experiment. This results would provide theory basis for the effective prevention and control of sheet erosion in purple soil area.