Abstract: With the continuous increase in the accessing proportion of renewable energy, the grid-connected system gradually tends to be a multi-infeed system and the grid strength is gradually weakened. The resonance problem will become one of the key factors which limits the improvement of the renewable energy penetration rate. Therefore, with the constraints on harmonic resonance, an optimal allocation method is proposed to increase the maximum accessing capacity of multi-infeed renewable energy clusters. First, the impedance model of the grid-connected inverter with operation points is established, and the aggregation model of the generalized multi-infeed system is obtained based on the electrical network theory. Then, the extreme function of phase margin with respect to cluster capacity is constructed, and the extreme condition under which the cluster impedance sensitivity should be kept consistent when the stability margin is maximum under a certain capacity is obtained by using the Lagrange multiplier method. On this basis, aiming at the maximum support demand of the renewable energy of the regional grid under the resonance constraint, a cluster capacity threshold value solving and an allocation optimization methods based on the sensitivity collaboration are proposed, and the complexity of the proposed method is analyzed. The proposed method is simple and efficient, and the computing power demand is small during capacity planning. Finally, the feasibility of the theoretical analysis and proposed method is verified by the cases of IEEE 9-bus and IEEE 33-bus regional microgrids in the real-time digital simulation hardware-in-the-loop.