  Homes' law, $\rho_s = C \sigma_{\mathrm{DC}} T_c$, is an empirical law
satisfied by various superconductors with a material independent universal
constant $C$, where $\rho_{s}$ is the superfluid density at zero temperature,
$T_c$ is the critical temperature, and $\sigma_{\mathrm{DC}}$ is the electric
DC conductivity in the normal state close to $T_c$. We study Homes' law in
holographic superconductor with Q-lattices and find that Homes' law is realized
for some parameter regime in insulating phase near the metal-insulator
transition boundary, where momentum relaxation is strong. In computing the
superfluid density, we employ two methods: one is related to the infinite DC
conductivity and the other is related to the magnetic penetration depth. With
finite momentum relaxation both yield the same results, while without momentum
relaxation only the latter gives the superfluid density correctly because the
former has a spurious contribution from the infinite DC conductivity due to
translation invariance.
