Abstract: The study of reactive power generation mechanism ＆ characteristic of doubly fed variable speed constant frequency（DFVSCF） wind power generator is important to improve its grid-supporting operation capability and grid’s voltage stability.From the equivalent circuit of doubly fed induction generator（DFIG）,the balance equation of reactive power was deduced.Based on the balance equation,this paper first discussed the reactive power conversion relationship between stator and rotor whose frequencies are different,then analyzed the mechanism of the flexible and strong capacity of DFIG in reactive power regulation.It further investigated the reactive power characteristic of DFIG under different operation conditions,and emphatically summarized the influence of slip rate and stator reactive power on rotor reactive power.At last,simulation and experiment were conducted to verify the validity and correctness of the analysis and conclusion.