The drag force of buildings in urban environment represent a complex and critical issue. Currently, most research usually regards buildings with uniform heights, ignoring the effect of the non-uniformity of building heights on the drag force distribution. To address this, this study proposes a height stratification method to calculate the sectional drag coefficient of buildings with non-uniform heights, C_dz. This method employs a sectional correction factor β_z to adjust the drag coefficient of buildings with uniform heights to C_dz of buildings with non-uniform heights. Subquently, wind tunnel experiments are then conducted to investigate the effects of building height category N, layer type, and layout on the sectional drag coefficient of individual buildings and the total building array. The results show that the non-uniformity of building heights has a significant impact on the flow adjustment process. When the building height category, N, is 2 or 3, the layer layout has a minimal impact on β_z. However, when N increases to 4, β_z values of staggered layouts are higher than those of square layouts. When using the height stratification method to calculate C_dz of buildings with non-uniform heights, β_z requires further parameterization if N≥4. The outcome of this study provide theoretical support for estimating drag force in urban buildings, enhancing the accuracy of building effect parameterization, and improving the precision of urban weather forecasting and pollutant dispersion calculations.