Vibration‐induced fluidization (ViF) is a phenomenon where a granular medium completely loses shear resistance or flows continuously under vibration and thus behaves like a fluid without invoking remarkable excess pore pressure. This paper attempts to investigate ViF through a series of modified triaxial tests and using an extended shear‐transformation‐zone (STZ) model that correlates macroscopic plastic deformation to the motion of internal mesoscopic weak spots (i.e., STZs) within granular materials. The test results revealed that the ViF may take place when the vibration is applied at either critical or non‐critical states. Theoretical analyses using the extended STZ model show that the vibration intensity required to cause fluidization increases linearly with the initial quasi‐static shear stress level at which vibration is imposed. The model results are generally consistent with experimental data, indicating that the extended STZ model has a desirable performance in simulating the fluidization of granular soil subjected to quasi‐static shearing and vibration simultaneously.