The combinative energy between two structural blocks in La2-xMxCuO4 (M=Ba, Sr), with different M concentration, has been calculated with holes in different positions in the CuO2 planes on the basis of a block model. The relationship between the combinative energy and superconductivity has been investigated. The results indicate that there is an interesting correlation among the combinative energy, the Tc value, and the positions of the doped holes, which are originated from the substitution of Ba2+ or Sr2+ for La3+. Although there are some similarities in correlation between La2-xBaxCuO4 (0.03<x<0.25) and La2-xSrxCuO4 (0.075<x<0.3), there are also some notable differences which may be originated from different properties of the substituted elements: barium and strontium. The results not only suggest that the interaction between perovskite-type and rocksalt-type blocks plays an essential role in high-Tc superconductivity, but also give us some clues of the influence of the position of the holes within the CuO2 plane.