To study the wind pressure characteristics and flow mechanism of square columns due to flow interference，taking the tandem square columns as the research object，large eddy simulation method is applied under the condition that Reynolds number Re = 8 × 104 and spacing ratio P/B=1.1~5. The influences of spacing ration on wind pressure coefficient，aerodynamic coefficient，non-Gaussian feature of wind pressure，and wind pressure correlation of the columns are discussed. The relationship between flow pattern and non-Gaussian characteristics of wind pressure is revealed. The results show that three major regimes are distinguished along with various spacing ratios，namely single bluff-body regime，shear layer reattachment regime and co-shedding regime，which are closely related with the specific wind pressure patterns. In the single bluff-body regime，the wind pressure near the recirculation zone between two columns shows significant non-Gaussian feature，whose correlation of wind pressure is strong. The shear layer reattachment regime，however，shows a weak vortex shedding in near wake，accompanied by a small wind pressure correlation but a large region of non-Gaussian wind pressure. Finally，in the co-shedding regime，due to vortex shedding of the upstream cylinder，the wind pressure on the side surface of two columns has a strong correlation and there is a large region of non-Gaussian wind pressure on the side and leeward surfaces of the downstream cylinder.