To investigate the influence of turbulence characteristic, structure dimension and separation distance on spanwise correlation characteristics of fluctuating along-wind loads acting on the rectangular building, the surface pressure fluctuations on a rigid model with rectangular cross-section were measured synchronically in the simulated atmospheric boundary layers. The distribution characteristics of coherence function of fluctuating along wind loads and oncoming turbulence were also studied. The correlation of unsteady along-wind loads and wind fluctuations, and the fluctuating pressures acting on windward side and leeward side were compared through present experiments. A modified expression of a coherence function of fluctuating along-wind loads on rectangular high-rise building was proposed by considering various parameters, including windward width of structure, spatial spacing and incoming wind characteristics. The measured results show that the fluctuating along-wind loads are more correlated than the wind fluctuation. The correlation of fluctuating pressures on windward side is weaker than that of overall unsteady drag forces in the case of model whose width exceeds the stream wise dimension. The weak correlation of fluctuating wind pressure on leeward side can't be ignored at a small separation distance. So the conventional coherence model of turbulence is unsafe for predicting the fluctuating along-wind loads of the high-rise buildings.