The invention discloses an analysis method for influence of a constant reactive power outer ring on stability of a convertor grid-connected system. At present, the analysis of the influence of the constant reactive power outer ring and the parameters thereof on the stability of the grid-connected system of the converter is not reported. The technical scheme adopted by the invention comprises the following steps of: establishing a converter impedance model and a power grid impedance model which adopt constant reactive power control, enabling the converter impedance model and the power grid impedance model to be equivalent to form a two-port network, enabling the converter impedance model and the power grid impedance model to form a closed-loop system with two inputs and two outputs throughthe series connection property of the two-port network, obtaining a closed-loop characteristic equation, and analyzing the influence of constant reactive power outer ring dynamics and parameters on the small interference stability of the converter grid-connected system. The method can effectively determine the influence of the set constant reactive power outer ring parameters on the stability of the grid-connected system of the converter, and avoids the problem of instability caused by improper selection of the constant reactive power outer ring parameters.