For the multi-propeller aircraft with distributed electric propulsion (DEP) configuration, a method to improve the lift-to-drag ratio of the wing was developed by optimizing the propeller slipstream. A propeller design method which can obtain the target induced velocity distribution was proposed. Based on the panel method, an aerodynamic program Prop-wing that can quickly calculate the propeller-wing interference was developed. An efficient optimization method based on Kriging surrogate model was established to obtain the optimal induced velocity distribution and raise the lift-to-drag ratio of the wing. The optimization results showed that the larger axial induced velocity near the propeller hub meant the larger lift drag ratio of the downstream wing. When the power of the propeller was not limited, the optimized propeller can reduce the drag of the downstream wing-segment by 1875% and increase the lift-to-drag ratio of wing-segment by 2563% compared with the propeller with the minimum energy loss; when the power of the optimized propeller was limited, the lift-to-drag ratio of the wing-segment increased to 962%. Although the lift-to-drag ratio is raised at the cost of propeller efficiency reduction, the research still provides an idea for the use of distributed propeller slipstream.