Abstract: The oscillatory characteristics of power system may be influenced by the dynamic interaction between the doubly-fed induction generators (DFIGs) and the synchronous generators (SGs). The existing study focuses on the sensitivity of the oscillatory modes to outputs of the SG, but the influence of the reactive power of the DFIG on the oscillatory modes has not been studied yet. This paper derives a small-signal stability model of power system with the DFIG. The elements of state matrix affected by the reactive power of the DFIG are decided, and the relationship between the eigenvalues and the bus voltages is derived. With the help of the power flow equation, the sensitivity of bus voltages to the reactive power of the DFIG is found. Finally, the analytical expression of the sensitivities of the weakly damped modes to the reactive power of the DFIG is newly proposed. The research results show that the improvement effect of DFIG reactive power and SG output adjustment on oscillation stability is similar, and DFIG reactive power does not change all weakly damped modes in the same direction. Multi-mode coordination should be considered when adjusting DFIG reactive power.