Abstract: Short-circuit ratio（SCR） is an important indicator to measure the grid-connected strength of power access points. The probability of oscillation and voltage instability for renewable energy power plants connected to the grid with low SCR is higher.First, for the scenario of the grid-connected renewable energy cluster, this paper analyzes the applicability and deficiencies of calculation methods of weighted SCR, composite SCR and equivalent SCR that are commonly used. An improved equivalent SCR calculation method for the renewable energy cluster considering reactive power output of renewable energy, static var generators,impedance angle and initial phase angle is proposed. Then, based on a simple network, the relationship between the proposed calculation method and the conventional SCR is proven, and the influence of the reactive power compensation method on the equivalent SCR is analyzed. Finally, combined with typical calculation examples and actual renewable energy base with ultra-high voltage DC transmission project, assessment and application study of power grid strength based on improved equivalent SCR is carried out, and the effect of distributed condensers on strengthening the grid-connected point strength of renewable energy power plants is further analyzed.