Abstract: To simplify the modeling of shallow-water waveguides with wedge-shaped seabeds, this study investigates the influence of seabed slope on the near-surface acoustic field. Numerical simulations of acoustic field distributions over both flat and wedge-shaped seabeds were conducted under three representative sound speed profile (SSP) conditions: isovelocity, positive-gradient, and negative-gradient environments. The results indicate that the variation trend of the near-surface acoustic field is only weakly affected by seabed topography. Using a transmission loss (TL) difference of no more than 3 dB as the criterion, the slope range within which a wedge-shaped seabed can be approximated as flat was determined by comparing TL distributions in the two environments. The results show that when the acoustic frequency is below 1 kHz and the SSP is either isovelocity or positive-gradient, wedge-shaped seabeds with slopes not exceeding 0.06° can be approximated as flat seabeds; moreover, the allowable slope range for the flat-bottom approximation increases with increasing frequency. In contrast, under negative-gradient SSP conditions, the approximation criterion exhibits a more complex dependence on source depth and frequency. For a source depth of 10 m, the maximum slope angle that can be approximated as a flat seabed decreases with increasing frequency, whereas for source depths of 75 m and 150 m, the allowable slope range increases with increasing frequency.