Based on a block model, separating the unit cell of YBa2Cu3O7-[delta] into perovskite and rock salt blocks, the combinative energy between the two blocks in the YBa2Cu3O7-[delta] with the different [delta] value, from 0.07 to 0.62, was calculated. A close relationship between the superconducting transition temperature and the combinative energy in YBa2Cu3O7-[delta] is established, and the change of the combinative energy is closely related to the transformation from orthorhombic I to II. The results also give a clue to reconsider the role of the orthorhombic I and II in YBa2Cu3O7-[delta]. The calculation of the holes in different planes supplies abundant information about the charge distribution in YBa2Cu3O7-[delta], which may possibly connect the electronic phase diagram and the fluctuations of the stripe phase. The results show that the interaction between the two blocks is of great importance for high Tc superconductivity.