A new energy cluster grid connection system has to encompass a certain number of conventional power sources that provide adequate short-circuit capacity to support the system voltage. However, excessive start-up capacity will reduce the new energy consumption space, so rationally optimizing the start-up mode of conventional unit is crucial to maintaining balance between new energy consumption and grid strength. To solve this problem, based on the short-circuit ratio index calculation method, a critical short-circuit ratio index constraint is used to build the coupling model between the start-up mode of a conventional unit and the strength of the new energy grid connection system. Then given that the ultimate grid connection strength requirements of new energy based equipment are satisfied, the optimization model for minimum start-up mode of a unit is devised to maximize the consumption of new energy, and the hybrid strategy of combining a genetic algorithm and CPLEX solver is used for the solution. Lastly, a new energy collection and transmission terminal system project in three northern regions of China is used as an example to demonstrate the effectiveness and superiority of the method.