In the research of control strategy of upgrading Liaoning power grid automatic voltage control system, taking the power grid reality into consideration, this paper improves the method of partitioning and the principle of choosing the key node and controllable pilot node. To solve the problems such as: one needs to artificially determine the number of partitions, it is possible that isolated node be as a whole partition, and there are still few unreasonable nodes in partition results, a pre-partition-correction method based on conditional clustering analysis is proposed. The voltage-sensitive critical node, together with controllable pilot node, be as monitoring nodes which are mainly monitored and regulated in each partition. And this paper also proposes the control principle of the critical node. After testing the method by applying it in the 220 kV system of Liaoning power grid, a desired result which meets the work requirements is got.