There are deficiencies in evaluating the complex mechanism of the mutual effects between large-scale new energy and the power grid by traditional power grid evaluation systems. Thus a performance evaluation index system is established considering large-scale new energy access. First, based on the key characteristics of the new power system and considering all parts of “power supply, grid, load and energy storage”, a power grid performance evaluation index containing connection, coordination, adaptation and carrying capacity levels can be set up. In addition, it explicitly expresses the statistical or calculation method for each index. Secondly, the AHP-CRITIC method is used to enable subjective and objective weights, and investigate the conflict and changeability among different indices based on the objective property of data from the power grid and computing standard deviation/Pearson correlation coefficient to highlight the scientific features on setting index weights. Finally, the index system for the data from new energy and the power grid in one city is surveyed and computed. The effectiveness of the proposed index system and evaluation method is shown through comparison and analysis. Some development proposals for weak parts of the power grid are proposed on the basis of the indicator’s sensitivity.