The examination of the dynamic characteristics of water vapor and energy exchange under the backdrop of global climate change is crucial for the sustainable utilization and management of water resources, particularly in agricultural regions where water is a scarce commodity. Based on the water and heat flux data and meteorological information collected by the Bowen ratio flux column of the Giant Juncao (Cenchrus fungigraminus) ecosystem in the semi-arid region of northwest China in 2022, the energy balance method and plate heat flux method were used to calculate the energy exchange and evapotranspiration indicators, and the changes of energy balance and evapotranspiration under different weather conditions were explored. The influence of Giant Juncao (Cenchrus fungigraminus) on surface energy balance; The main driving factors of evapotranspiration and Bowen ratio change. The findings show that solar radiation during summer weather exhibits a single-peak pattern, with peak intensity ranked as clear > cloudy > rainy days. Net radiation follows a single-peak trajectory on clear days, varies significantly on cloudy days, and forms a 'concave' pattern on rainy days. The mean net radiation is highest on cloudy days, followed by rainy and then clear days. Specifically, cloudy days register 527.41 W/m<^>2 more net radiation than clear days and 343.28 W/m<^>2 more than rainy days every 10 minutes. Surface reflected radiation, under all weather scenarios, adheres to a single-peak pattern. There is a positive correlation between solar radiation, temperature, and surface reflectance, with the presence of Giant Juncao enhancing reflectance. The average annual surface reflectance of the Giant Juncao ecosystem is 0.28, with the following order: clear days < cloudy days < rainy days. Latent heat flux manifests a single-peak pattern on clear days, a wave-like trend on cloudy days, and its magnitude on rainy days is contingent upon rainfall timing, showing reduced latent heat flux during rainfall and an increase in the atmosphere's latent heat flux during dry spells. The diurnal range of sensible heat flux is greatest on clear days, followed by cloudy and rainy days, mirroring the pattern observed in soil heat flux. Both the Bowen ratio and evapotranspiration exhibit a single-peak variation across all weather conditions. Evapotranspiration totals 0.74 mm on clear days, which is lower than the 1.41 mm observed on cloudy days but higher than the 0.45 mm on rainy days. The average Bowen ratio across different weather conditions follows the sequence: cloudy days > clear days > rainy days. Solar radiation emerges as the principal driver of evapotranspiration and the Bowen ratio, with additional influences from air temperature, wind speed, and soil moisture content under varying weather conditions. This study of energy partitioning within the Giant Juncao ecosystem under diverse weather scenarios lays the groundwork for future propagation and cultivation of Giant Juncao in the equatorial zone and the semi-arid regions of Northwest China.