The two-body(core+2n) cluster structure was implemented to describe the two-neutron halo nucleus~(14 )Be, where the core12 Be was assumed inert and at a ground state and the dineutron was assumed at a pure 2S0 state. Based on such a structure the three-body continuum-discretized coupled-channel(CDCC) calculation was successfully used to deal with the~(14) Be breakup reactions of~(14)Be+Pb at 35 Me V/u. Consequently, we modeled the kinematically complete measurement experiment of this reaction with the help of Geant4. With the simulation data the relative energy spectrum was constructed by the invariant mass method and B(E1) spectrum was extracted using the virtual photon model. The influence of the target thickness and detector performance on the energy spectroscopy was investigated. The two-body (core + 2n) cluster structure was implemented to describe the two-neutron halo nucleus ~ (14) Be, where the core12 Be was assumed inert and at ground state and the dineutron was assumed at a pure 2S0 state. Based on such a structure of the three-body continuum-discretized coupled-channel (CDCC) calculation was successfully used to deal with the (14) Be breakup reactions of ~ (14) Be + Pb at 35 Me V / u. we modeled the kinematically complete measurement experiment of this reaction with the help of Geant 4. With the simulation data the relative energy spectrum was constructed by the invariant mass method and B (E1) spectrum was extracted using the virtual photon model. The influence of the target thickness and detector performance on the energy spectroscopy was investigated.