Oscillation instability is easily induced by grid-following (GFL) converters under weak grid conditions. However, system stabil-ity can be significantly enhanced by the integration of a certain proportion of grid-forming (GFM) converters within renewable energy stations. Consequently, the capacity ratio of GFL to GFM converters is regarded as a critical factor governing system sta-bility. To address this, an analytical model for the capacity alloca-tion based on the critical short circuit ratio (CSCR) is proposed in this paper. Initially, positive- and negative-sequence impedance models for both GFL and GFM converters are established to facilitate the comparison of their sequence impedance character-istics. Subsequently, a three-port equivalent model of the hybrid grid-connected system is constructed. Through sensitivity analy-sis, the dominant control parameters affecting the interactive stability of the system are accurately identified. Furthermore, by integrating the generalized Nyquist stability criterion with the CSCR boundary conditions required for maintaining the stability of grid-connected equipment, an analytical model for the mini-mum integration ratio of GFM converters—which ensures the small-signal stability of the system—is rigorously derived. Fi-nally, the validity of the theoretical analysis is verified through electromagnetic transient simulations. It is demonstrated by the research results that the required critical GFM capacity can be accurately calculated by the proposed analytical model, thereby facilitating the rightward shift of the system''s interactive reso-nance frequency band into the stable region. Through this con-figuration, the phase margin of the system is significantly en-hanced, and the broadband interactive instability under weak grid conditions is effectively suppressed.