The LUMO-HOMO energy gaps in YBa2Cu3O7 have been calculated with density functional method (DFT) on a cluster model of unit cell in a wide range of temperatures (5 K~300 K). The results show that the superconducting energy gap (2?(T)) is about 80 meV at Tc (93 K), and decreases smoothly as the temperature increasing. It reaches the minimum at Tc and exhibits pseudogap above Tc. The pseudogap value reaches the maximum at T*(120 K) when the temperature increasing. The calculations by the cluster model of YBa2Cu3O6 unit cell show that the energy gap is about 102meV with characteristic gap of semiconductor.