  Topological semimetal, hosting spin-1 Weyl point beyond Dirac and Weyl
points, has attracted a great deal of attention. However, the spin-1 Weyl
semimetal, which possesses exclusively the spin-1 Weyl points in a clean
frequency window, without shadowed by any other nodal points, is yet to be
discovered. Here, we report for the first time a spin-1 Weyl semimetal in a
phononic crystal. Its spin-1 Weyl points, touched by two linear dispersions and
an additional flat band, carry monopole charges (-2,0,2) or (2,0,-2) for the
three bands from bottom to top, and result in double Fermi arcs existing both
between the 1st and 2nd bands, as well as between the 2nd and 3rd bands. We
further observe robust propagation against the multiple joints and topological
negative refraction of acoustic surface arc wave. Our results pave the way to
explore on the macroscopic scale the exotic properties of the spin-1 Weyl
physics.
