The integration of a large number of renewable energy grid-connected converters into the power grid can easily trigger small-signal instability, posing a serious threat to the safety and stability of the system. The existing small-signal stability analysis using the impedance method, based on a multi-machine equivalent mechanism, can only provide an analysis of the factors influencing stability and cannot identify the key weak grid-connected units that affect stability. This paper proposes a method for identifying small-signal stability weak grid-connected units in a renewable energy multi-site system based on the generalized Nyquist criterion (GNC). Firstly, based on the stability analysis approach of GNC, multiple renewable energy sites with different control parameters are decoupled into multiple single-site subsystems. Then, a stability criterion is constructed for each subsystem to analyze the small-signal stability of each subsystem. Finally, the subsystem with the weakest stability is identified based on the small-signal stability of each subsystem. The research results show that, compared with existing methods, this method can more accurately and quickly identify small-signal stability weak grid-connected units, providing targeted guidance and suggestions for improving system stability