Abstract: To investigate the effects of different new types of blade-tip on transonic acoustic characteristics of a helicopter rotor, numerical analyses about the impacts of blade-tips on the high-speed impulsive (HSI) noise characteristics have been carried out by taking the UH-1H model rotor as baseline. A CFD simulation method is developed by solving the compressible Reynolds-averaged Navier-Stokes (RANS) equations with Baldwin-Lomax turbulence model, and a high-precision Roe-MUSCL scheme and high-efficiency implicit LU-SGS scheme are employed for spatial and temporal discretization respectively. Based on the validation of CFD method, a robust FW-H_pds method based on the penetrable data surface is established for predicting rotor HSI noise, and the transonic acoustic characteristics of UH-1H model rotor have been simulated to verify the effectiveness of the present method. Based on these methods, the influences of Mach number on the phenomenon named "delocalization" nearby the blade tip and the HSI noise characteristics are analyzed, and the generation mechanism of transonic noise is revealed by the comparisons of the monopole noise and quadrupole noise. Then, the influences of both sweep-back and sweep-forward blade-tip on inhibiting rotor transonic acoustic characteristics are analyzed at a transonic state respectively. The numerical results indicate that the serious delocalization phenomenon and the HSI noise radiation occur strongly with the increase of the blade-tip Mach number. Compared with rectangular blade, the rotors with sweep-back or sweep-forward blade-tip can reduce HSI noise level at a transonic state by suppressing the supersonic flow and delaying the occurrence of delocalization effects. Furthermore, sweep-forward blade-tip has a more remarkable effect on inhibiting delocalization effects by driving supersonic flow region to move to inside of blade.