Abstract: A method for estimating wind-induced fluctuating internal pressure in the frequency domain is proposed and wind tunnel tests were carried out to verify the method. Based on Bernoulli equation, nonlinear differential equation for dynamic internal pressure is derived and random vibration theory combined with iteration algorithm is used to obtain the solution. Numerical examples are provided to investigate frequency response characteristic of internal pressure and the influences of opening ratio, opening number and opening position on fluctuating internal pressure. A series of low-rise building models with various openings were designed and wind tunnel tests were conducted. Experimental results agree well with theoretical ones. It is shown that the internal pressure fluctuation is determined by the frequency response characteristic of the cavity-orifice dynamic system and orifice pressure spectrum for single opening structures. For structures with multiple openings, wind pressure correlations at orifices also affect fluctuating internal pressure considerably.