Three-phase load imbalance is a relatively common problem in distribution network. In order to study the vibration characteristics of distribution transformer under three-phase unbalance condition, this paper theoretically analyzes the vibration characteristics of iron core and winding and the vibration propagation characteristics of winding, uses finite element software to study the variation of magnetic induction intensity and winding electromagnetic force when three-phase load balance and unbanlance. Meanwhile, a transformer vibration measuring platform is set up to collect vibration signals of transformer under rated load of single-phase and two-phase at different positions of three-phase. The results show that the flux density in the core is basically unchanged under the condition of three-phase load unbalance, and the load unbalance will not affect the high-frequency component of transformer vibration signal. The unbalance degree of the three-phase load is the same, and the influence degree of the unbalance phase on the same vibration measuring point is different under different locations.