The invention discloses a continuously adjustable reactive power source AVC (automatic voltage control) control instruction selection method and system. The method includes the following steps that: 1) a master station AVC system obtains the state expected values of continuously adjustable reactive power sources in a region according to SCADA real-time data and state estimation results, wherein the state expected values of the continuously adjustable reactive power sources include control target voltage expected values and control target reactive power output expected values; 2) a part of the continuously adjustable reactive power sources are selected as power grid dynamic reactive power support points according to dynamic support factors to issue control target voltage expected value remote call instructions, and the other continuously adjustable reactive power sources issue control target reactive power output expected value remote call instructions; and 3) a first-level controller controls the reactive power output of the reactive power sources according to received voltage or reactive power remote call instructions. With the method and system of the invention adopted, a power grid dynamic reactive power supporting requirement can be satisfied, and the problem of reactive power imbalance caused by the difference of the adjustment speed of the continuously adjustable reactive power sources can be solved, and the safe, economical and high-quality operation of a power grid can be ensured.