It's important to understand the land-atmosphere interactions over the semi-arid area of Loess Plateau, which featured by special climate and unique underlying surfaces. Seasonal variability of precipitation,soil moisture, radiation,albedo and energy fluxes,especially the influence of rain,soil moisture and agricultural production activities to the energy partition,were analyzed systematically,using a full year observations over a rain-fed cropland at the Pingliang Land Surface Process & Severe Weather Research Station. The results showed that the seasonal distribution of precipitation was uneven,gave rise to the significant seasonal differences in soil moisture. Radiative components had seasonal cycles. Shortwave radiation fluctuated with weather conditions,while longwave radiation was less affected. Surface albedo had significant seasonal variations:the maximum midday mean value(0.83)occurred after snow,then dropped to less than 0.2 during crop growth,afterwards,it fluctuated with precipitation after crop harvest. There was a linear relationship between albedo and soil moisture. Turbulent energy fluxes had diurnal cycle and seasonal variations. The partition of energy was largely affected by the changes in precipitation as well as agricultural production activities. The main consumer of the available energy was different among months,monthly mean diurnal cycle of the latent(sensible)heat flux attained maximum in May(April),which was 240.8(192.5)W·m~(-2). On an annual scale,the largest consumer of midday net radiation was sensible heat flux,which accounted for about 35% of Rn. While the latent heat flux was about 32% of Rn,which was lower than irrigated croplands. During the rapid growing season of winter wheat(March to May),the average midday LE/Rn was about 34%,which was much lower than irrigated winter wheat agro-ecosystem, indicating that it was water limited in our study site.