Cascading wind farm trips have brought new challenge to the wind power integration.Traditional reactive power optimization can achieve a desirable control result，but voltage security violation usually happens after N-1contingency because of the redistribution of power flow and slow response by the reactive power compensator.Therefore，a reactive power optimization model is set up with security constraints，aiming to maintain the voltage within the security region under both normal condition and N-1contingency.Besides，Benders decomposition method is employed to solve the complex model， dividing into one master and some slave problems.Iterative method is used between master and slave problems to obtain the optimal solution.Practical power grid with nine wind farms is tested，and the comparison of security constrained optimal power flow（SCOPF）and traditional optimal power plow shows that the SCOPF has better effect，which can maintain the voltage security under both normal condition and N-1contingency.So it is an effective method to prevent cascading faults of multiple wind farms integrated into power grid.Finally，the relationship of maximum wind power integration，wind farm capacity and reactive power capacity of wind units is fully studied to provide certain help for the operation of wind farm.