  When the Lyapunov exponent $\lambda_L$ in a quantum chaotic system saturates
the bound $\lambda_L\leqslant 2\pi k_BT$, it is proposed that this system has a
holographic dual described by a gravity theory. In particular, the butterfly
effect as a prominent phenomenon of chaos can ubiquitously exist in a black
hole system characterized by a shockwave solution near the horizon. In this
paper we propose that the butterfly velocity can be used to diagnose quantum
phase transition (QPT) in holographic theories. We provide evidences for this
proposal with an anisotropic holographic model exhibiting metal-insulator
transitions (MIT), in which the derivatives of the butterfly velocity with
respect to system parameters characterizes quantum critical points (QCP) with
local extremes in zero temperature limit. We also point out that this proposal
can be tested by experiments in the light of recent progress on the measurement
of out-of-time-order correlation function (OTOC).
