To explore the potential for increasing lift on low tip-speed rotors， a rotor performance calculation model is established. The flight data of the UH-60A helicopter are utilized to validate this model. Further research is conducted on the influence of the Gurney flap on the hovering and forward flight performance of the low tip-speed rotor. The results indicate that， in hover， Gurney flaps increase rotor thrust but with higher power consumption. The thrust coefficient rises by up to 12.00%， while the power coefficient increases by 7.98%. Under high-thrust conditions， Gurney flaps enable the rotor to maintain the same thrust as the baseline configuration at a reduced collective pitch， thereby significantly improving the figure of merit by 18.55%. In forward flight （100 km/h）， the thrust coefficient improves by 11.30%， but with greater power penalty （power coefficient increases by 18.64%）. Gurney flaps also improve the lift-to-drag ratio， with a maximum increase of 28.77%. For low tip-speed rotors， at a given thrust， Gurney flaps reduce the angle of attack and increase the lift-to-drag ratio， thereby improving rotor aerodynamic performance in high-thrust conditions.