Abstract: An aircraft with four turbo-propeller engines is characterized by low speed and relative high cruise lift coefficient.Winglets are utilized to improve the flow condition around the wing tips and increase the lift-to-drag ratio.CFD calculation and wind tunnel tests show that the lift-to-drag ratio at endurance cruise can be increased by 8%,while the lift-to-drag ratio at range cruise can be increased by 4.8% after the optimization of geometric parameters.The results of CFD simulation about the aerodynamic characteristics of the winglet agree well with wind tunnel test results, which could be a convenient and economic method for further optimization of winglet geometry.