It is of great significance to evaluate the performance of green transformation for the economic transformation and green development of resource-based cities. Based on the theory of sustainable development, this paper constructs a comprehensive evaluation index system of green transformation performance of resource-based cities, measures the green transformation performance of 114 resource-based cities by principal component analysis, and then uses dagum Gini coefficient to investigate the gap and source of green transformation performance of different types of cities. The results show that: on the whole, the green transformation of resource-based cities has achieved remarkable results, the high value areas of transformation performance are concentrated in the northern and eastern coastal areas of China, and the performance mainly depends on the effect of economic transformation and social transformation; from the perspective of grouped samples, the economic, social and environmental transformation development of different types of cities has cyclical characteristics, but due to the four types of cities, the performance of green transformation of resource-based cities mainly depends on the effect of economic transformation and social transformation. The transformation effect of resource-based cities is different with different transformation ways. Further analysis shows that the overall gap of urban green transformation shows a narrowing trend. From the perspective of different types of cities, the intra group gap of growth and regeneration cities shows an overall widening trend, while the intra group gap of mature and decline cities shows a narrowing trend. The gap between growth and regeneration cities is the largest, with an average of 0.1585. The gap mature and decline between cities is the smallest, with an average value of 0.0858. The narrowing of intra group gap is the main factor of the overall gap narrowing.