Background Eco-economy sustainable development is an important part of China's sustainable development. At present, research on the eco-economic sustainability of ecological fragile zone in semi-arid desert area is relatively weak. Yulin city is located in the middle section of the farming pastoral ecotone in northern China and vulnerable to ecological environment. The 42% of its northern area is Mu Us Sandy Land. Studying the sustainable development of its eco-economic system is of significance for promoting environmental economic governance and sustainable development in ecologically fragile areas.

Methods Collecting the macroeconomic and social development data and meteorological data of Yulin city from 2008 to 2018, using the emergy analysis method, the original data was divided into 5 categories according to emergy elements: renewable resources, non-renewable resources, input flow, output flow, and waste flow. The emergy of different elements was calculated, the emergy analysis table was compiled, the eco-economic evaluation system was constructed, it included the comprehensive development index of social, economic and natural subsystems, and the eco-economic development and sustainability of Yulin city from 2008 to 2018 was evaluated.

Results 1) In general, from 2008 to 2018, the total use of emergy in Yulin city increased from 1.97×10²³ to 5.33×10²³ sej, and the emergy of non-renewable resources accounted for 80.49%-85.20%, belonging to the economic mode of high energy consumption. 2) From the perspective of social subsystem, the emergy per person of Yulin city increased from 4.60×10¹² to 1.22×10¹³ sej/m², increasing by 2.65 times. Emergy intensity was constantly strengthening, but the population carrying capacity decreased from 232 000 to 137 000, the ecological environment was not enough to support population development. 3) From the perspective of economic subsystem, the emergy money ratio decreased from 1.36×10¹³ to 9.17×10¹² sej/.The speed of economic development and urbanization was accelerated, but the emergy load ratio decreased from 10.13 to 7.18, the emergy production efficiency reduced. 4) From the perspective of ecological subsystem, the energy self-support ratio reached over 85%, the environment load ratio increased from 11.92% to 20.53%, and the environmental pressure was increasing. The emergy index for sustainable development ESID dropped from 253.0 to 163.60.

Conclusions The economic development of Yulin city mainly comes from the development and utilization of local non-renewable resources. The external output energy value is insufficient. In the long run, the energy utilization structure is unreasonable, the eco-economy system presents an unsustainable development trend, and the support capacity of system resources for economic development is constantly declining. Thus the sustainable ability of regional eco-economy can be improved from the aspects of regional industrial waste gas treatment, energy structure adjustment, external resource input, etc.