In order to make full use of the ability of photo voltaic (PV) units to regulate their own reactive power to participate in voltage stability control of power system, this paper takes full account of the interaction between power grid and PV power plant and proposes a multi-level reactive power control strategy based on sensitivity analysis for PV plant. Firstly, reference of reactive power is calculated combined with the analysis of reactive power and voltage sensitivity of PV power plant and the operation status of power grid. Secondly, reactive power command is allocated to each PV unit according to the reactive power margin. Finally, a reactive power control system model based on an actual PV plant project is established to verify the correctness of proposed strategy in this paper.