  Due to their possibility to encode information and realize
low-energy-consumption quantum devices, control and manipulation of the valley
degree of freedom have been widely studied in electronic systems. In contrast,
the phononic counterpart--valley phononics--has been largely unexplored,
despite the importance in both fundamental science and practical applications.
In this work, we demonstrate that the control of "valleys" is also applicable
for phonons in graphene by using a grain boundary. In particular, perfect
valley filtering effect is observed at certain energy windows for flexural
modes and found to be closely related to the anisotropy of phonon valley
pockets. Moreover, valley filtering may be further improved using Fano-like
resonance. Our findings reveal the possibility of valley phononics, paving the
road towards purposeful phonon engineering and future valley phononics.
