The frequency response transfer function of different pipe lengths is determined with the pressure measurement system. Furthermore, effects of the pipe length on wind pressure coefficients and wind-induced response on a flat roof are investigated without the pressure correction. The results show that a short pipe usually amplifies the fluctuating wind pressure, and a long pipe reduces the pressure. Fluctuating wind pressure diminishes significantly with a very long pipe, especially at the high frequency; the effect of the pipe length on wind-induced response is less than that on wind pressure coefficients on the roof; the relationship between the pipe length and the calculation errors of wind pressure coefficients and wind-induced response is nonlinear and oscillating, and the calculation error is relatively smaller for the pipe length around 100cm; the wind pressure correction is necessary for most pipe lengths.