Abstract: According to Taylor’s Frozen Assumption about turbulence, an analytical solution of spectral density function of pressure fluctuation in across-wind direction was derived from the governing equation of flow movement in turbulence theory. All of the turbulence-mean components in the source term of pressure governing equation had been taken into account. If an appropriate turbulence integral scale is adopted, the spectrum density function value will correspond well to the results from full scale measurements. The function value near the basic natural frequency of building is larger than that from wind tunnel test. The displacement and the acceleration value evaluated with this fluctuating pressure load are larger than those from Japanese design code.