Flatbands, characterized by their dispersionless energy levels in electronic, magnetic, and phononicsystems, hold substantial potential for advancements in electronics and quantum information processing. Most flatbands exist in thermal equilibrium and cannot be easily created or annihilated externally, limiting their flexibility as switchable knobs for use in microelectronics and quantum applications. In this work, the generation of a coherent phonon flatband in a GaAs/AlAs superlattice is demonstrated using 800 nm femtosecond laser pulses. This coherent phonon flatband does not correspond to a phonon eigenmode at equilibrium and exhibits strong coupling with two branches of coherently excited longitudinal phonon modes. With molecular dynamics simulations, it was shown more generally that the coherent phonon flatband can be induced by coherently and spatially modulated optical excitations of superlattice structures.These results highlight a pathway for coherent phonon flatband creation in the time domain that can be generalized to various superlattice systems, potentially inspiring the realization of coherent flatband generation of other quasiparticles.