Abstract: The large-scale integration of renewable energy into the power grid leads to the decrease of system voltage support strength, which is usually characterized by its short circuit ratio (SCR). This results in stability issues such as static voltage stability problems and sub/super synchronous oscillation. Grid-forming (GFM) converters have effective voltage support capability, and thus equipping renewable energy stations with a certain proportion of GFM converters can improve the stability of the system. However, the analytical relationship between the capacity of GFM converters and the stability margin is unclear, which makes it difficult to estimate the required proportions of GFM converters theoretically. To fill this gap, this paper discusses the estimation method for the required capacity ratios between GFM converters and grid-following (GFL) converters to maintain small signal stability. First, based on the voltage-source equivalent analysis of GFM converters, the influence of the capacity ratios on the system strength and stability margin is analyzed through the generalized short circuit ratio (gSCR) index. Then, considering the practical engineering scenario of updating some wind turbines to GFM control or installing new GFM converters, the typical values of the capacity ratios are discussed based on typical parameters of step-up transformers and the related industry standards as boundary conditions. The validity of the conclusion is verified by simulation results of a typical multi-wind-farm system.