The nutrient uptake, photosynthesis and yield of different separation methods were measured to analyze resource competition from above-and below-ground interaction. The treatments included no shoot or root separation (T1), shoot and root separation (T2), root separation (T3), shoot separation (T4), sole maize (T5) and soybean (T6). The land equivalent ratios of grain yield and biomass were 1.23 and 1.20 for T1, 0.97 and 0.91 for T2, 1.01 and 1.02 for T3, 1.10 and 1.08 for T4, respectively. Competiveness of maize relative to soybean was 0.79 for T1, -0.08 for T2, 0.14 for T3 and 0.39 for T4, respectively. The nutrient competitive ratios of maize relative to soybean were 1.63, 1.92 and 1.50 for T1; 1.05, 1.03 and 1.06 for T2; 1.28, 1.32 and 1.27 for T3; 1.47, 1.43 and 1.36 for T4, respectively. Except the jointing stage, the Pn, Tr, Gs and Ci of maize were the highest for T1; and the values for T4 were the second; and the values for T2 and T3 were remarkable lower than that for T1. Except the branching stage, the parameters of soybean were the lowest for T1, and the values for T2 and T3 were significantly higher than that for T1. In summary, as for maize/soybean intercropping advantages, the interactions of above- and below-ground parts was greater than that under the action of a single factor, and there was greater role from below-ground part than above-ground part.