Abstract: For investigating and tracing the multi-bunch transverse coupled instability caused by beam impedance and evaluating the suppressive effect to the instability by the newly updated Transverse Feedback System during the upgrade process of Shanghai Synchrotron Radiation Facility (SSRF) PHASE II, transverse beam motion in different states were recorded by diagnostics tool of feedback processor in the system, by which the evolution of dominate instability modes were analyzed respectively in steady-state, injection transient and growing-damping process. Growth/Damp rate as well as dependence of growth rate and beam current were calculated. Also, performance of the feedback system was evaluated. These research results provide data support for machine operation optimization.