Aiming to understand eco-hydrological processes and boost water use efficiency in rainfed agroecosystem, a field experiment was conducted in non-mulched (CK) and mulched (PM) maize fields of eastern Loess Plateau to continuously monitor water and energy flux in the maize fields under CK and PM. Based on the monitoring results, diurnal and seasonal variations of water and energy flux as well as energy partitioning were investigated. The results indicated that energy fluxes presented typical diurnal and seasonal variations during the entire growing seasons. Net radiation (Rn) was dominated by latent heat flux (λET) during maize growing seasons while sensible heat flux (H) was the predominant component of Rn during non-growing seasons. Compared with the energy flux before rainfall, λET was increased significantly while H and soil heat flux (G) was decreased after rainfall in development stage, however, in late stage, the changes in soil water content resulted by rainfall did not increase λET significantly for the both treatments, which indicated seasonal distribution of rainfall had significant influence on energy budget of maize fields. Rn was the primary factor affecting λET, followed by average air temperature and vapor pressure deficit, wind speed and relative humidity had relatively minor influence on λET.