Context: Mixed cropping can increase and stabilize productivity. However, the effects of mixed cropping practices on system productivity stability and eco-efficiency can be positive in some cases and neutral or negative in others. Objective: This study was aimed at providing the selection basis of agricultural production systems by clarifying the mechanism of yield stability and greenhouse gas (GHG) emission reduction advantage in mixed cropping systems among different climatic regions. Methods: A 4-year field experiment (2020-2023) with five cropping systems [forage maize (Zea mays L.)/lablab (Lablab purpureus L.) mixed cropping (ML), forage sorghum (Sorghum bicolor L.)/lablab mixed cropping (SL), sole forage maize (SM), sole forage sorghum (SS), and sole lablab (LL)] and two study regions (irrigated region, IR; rain-fed region, RR) was conducted. Results: Results showed that dry matter yield (DMY), crude protein yield (CPY), and eco-efficiency index (EEI) were improved by 14.0 %, 16.5 %, and 79.0 %, respectively, in the irrigated region, with a decrease in productivity variation and GHG emission intensity (GHGI) by 16.8 % and 49.4 %, respectively, compared with those in the rain-fed region. In addition, mixed cropping significantly increased DMY and CPY by 34.7 % and 25.0 %, respectively, compared to the average values under the SM, SS, and LL treatments. Similar improvements were observed for yield stability, which reached a maximum value under the ML treatment. Furthermore, mixed cropping significantly improved EEI and reduced GHGI, where the ML treatment increased EEI by 50.5 % and reduced GHGI by 29.3 % compared with the corresponding forage maize monoculture. The highest sustainability index was observed for the forage maize mixed with lablab cropping system (0.84). Conclusions: Forage maize mixed with lablab is emerging as a promising agronomic strategy that efficiently utilizes water and nitrogen in the irrigated region and reduces rainfall-induced production variability in the rainfed region, which improves forage productivity and stability while reducing GHG emissions. Implications: Our study highlights the reasons that the effects of mixed cropping systems on stability and ecoefficiency vary, providing scientific guidance for recommending forage production practices.