Substitutional doping lanthanide ions (Ln3+) in CsPbX3 has been proven to be an efficient strategy for expanding the properties of the perovskite (PVK). Here, erbium (Er3+) uniformly doped CsPbX3 perovskite microplates are grown through a chemical vapor deposition method. Two fluorescence peaks at 430 and 520 nm which respectively correspond to the PVK and Er3+ emissions are observed. The time-resolved photoluminescence of both PVK host and Er dopants demonstrates that trap states play a critical role in facilitating the energy transfer between the PVK host and the Er dopants, which is vital to sensitizing the Er3+. A photophysical model was put forward to comprehensively describe this trap-mediated energy-transfer process, and the dynamics processes are modeled using correlated rate equations. The rates of the carrier's relaxation and energy transfer are respectively obtained as 6.6 and 49 ns-1, and a total energy transfer efficiency was obtained as ∼32.6%.