  We study the bulk viscosity of strange quark matter (SQM) in a quasiparticle
model at finite chemical potential by extrapolating the previous quasiparticle
model of finite temperature lattice QCD. The more proper bulk viscosity
coefficient can be given in this model where chemical potential $\mu$ and
coupling constant $\emph{g}$ are interdependent. We also apply our result to
determine the critical rotation of strange stars by r-mode instability window.
Our model is compatible to the millisecond pulsar data for a wide range of mass
and radius of the stars.
