In this article, we fabricated Ce3+, Yb3+-coped yttrium aluminum garnet (YAG) inverse opal photonic crystals by a self-assembly technique in combination with a sol-gel method. The photonic band gap was located at 545 nm. With the influence of the photonic band gap, cooperative down-conversion energy transfer process of Ce3+-Yb3+ was investigated. It is significant that the energy transfer efficiency between Ce3+ and Yb3+ is enhanced from 29.6% to 47.6% by suppression of the yellow spontaneous emission of Ce3+. The mechanisms for the influence of the photonic band gap on cooperative down-conversion process of Ce3+ and Yb3+ are discussed.