Power transmission and transformation engineering is a pivotal aspect of power grid construction and an important link to power grid planning. It holds substantial relevance to the economic to the economic, social, and environmental benefits of China’s power construction. Consequently, the design of power transmission and transformation engineering, as the source of power transmission and transformation project construction, holds notable importance. In this paper, the evaluation system of design capability for power transmission and transformation engineering was established from the dimensions of basic hard strength, design bearing capacity, result quality control, deviation control, and technological innovation capacity. The weight of the evaluation indicators of the design capacity of power transmission and transformation engineering is determined based on advanced design units and data analysis combined with expert experience. On this basis, the corresponding evaluation system of design capability was developed. The application of this system provided accurate basic data for the evaluation of design capabilities in power transmission and transformation engineering. The design capability assessment report issued can help provincial companies comprehensively evaluate the design capabilities of various design units, thereby promoting standardized management of design units.