Abstract: Energy is not only the power base, but also a basic function of ecological systems. Analyzing the characteristics of agro-ecosystems via energy flow analysis can ensure comprehensive component objectivity. The energy output level of any agro-ecosystem is an energy flow key index. Using the characteristic indexes of energy flow, different function characteristics of agro-ecosystems were analyzed. The 21st century view emphasized the coordinated development of resources, environment, economy and society. This eventually gave rise to a new mode of sustainable agricultural production, promoted mainly through straw return to farmlands. Although straw return may not make full use of crop straw resources, it reduces environmental pollution. It is therefore the inevitable mode of sustainable economy development in the Central Shaanxi Plain (CSP). To build further understanding into the energy-flow characteristics of wheat/corn straw-return mode in farmland ecosystems, eco-theory and system analysis were used to investigate different straw-return modes in CSP. Then supplemental energy inputs, outputs and transformation efficiencies of different straw-return modes were analyzed and discussed. The results showed that total energy input (7.12×10¹⁰ J·hm^-2), organic energy input (5.44×1010 J·hm^-2), organic/inorganic energy value (3.25) and CREF (0.76) of WH-MC mode (wheat high stubble mulching and straw returning to field plus maize straw chopping and direct returning to field) were highest. While WC-MC mode (both wheat and maize straw chopping and direct returning to field) was the effective in solar energy use (0.669%), WN-MN mode (no turning of both wheat and maize straw) was the most in energy conversion (6.05). In summary, the energy analysis of the functions of the straw-return modes produced better results than the no-straw-return modes. The WH-MC mode had the highest integrated score (0.792). This showed that WH-MC was the optimal mode with the highest eco-efficient plant production, recommended for promotion and wide adoption in CSP.