The invention provides a multiphase flow empennage motion simulation mechanism in a water tunnel experiment. The multiphase flow empennage motion simulation mechanism includes a driving motor which is arranged outside a water tunnel wall face and performs linear motion, an oscillating rod connected through an adapter with an output end of the driving motor which performs linear motion, a sliding block mounted on an end part of the oscillating rod, a pull rod fixedly connected with the sliding block, an empennage rotating rod hinged to an end part of the pull rod and an empennage shaft fixedly connected with an end part of the empennage rotating rod, an empennage is arranged on the empennage shaft, a rectification support structure is arranged within the water tunnel wall face, the oscillating rod is located in the rectification support structure, and the sliding block, the pull rod and the empennage rotating rod are externally provided with a fairing. The multiphase flow empennage motion simulation mechanism in the water tunnel experiment is simple in structure and easy to realize, and simulates a process of vacuole multiphase flow disturbance by empennage motion in a water tunnel by means of the driving motor outside the water tunnel.