Abstract: The scale limit, transient overvoltage, control instability and other issues may occur when the large-scale power electronic equipment such as renewable energy system and VSC-HVDC is connected to a weak power system. The severity of these problems is related to the system strength. In this paper, based on the scenarios of power system with power electronic equipment, the construction methods and applications of quantification indexes were summarized. The concept of system strength was expounded by analyzing the key characteristics of power system and the relationship with quantification indexes. The short circuit ratio (SCR) index is an important quantification index and its construction methods can be diversified according to the characteristics of the system with power electronic equipment. The critical short circuit ratio (CSCR) is the criterion to divide the system strength and its calculation methods. The numerical inconsistency were analyzed. Next, the influence of impedance ratio (IR) on the system strength was analyzed by deducing the influence of IR on CSCR. This paper summarized the problems of existing quantification indexes, and suggested that the SCR index should be taken as the main index and the IR index as the auxiliary index in the system strength evaluation, so as to provide a reference for follow-up researches on measuring the system acceptance capacity of power electronic equipment.