Using multiple daily data of GSWP (Global Soil Wetness Project), GLDAS (Global Land Data Assimilation System), AMSR-E (Advance Microwave Scanning Radiometer-EOS) soil moisture, and in-situ observations, the method of the sliding t test is applied to analyze characteristics of seasonal variations of the underlying surface variables for the purpose to better understand energy and water cycles over the Tibetan Plateau (TP). The analysis reveals that the seasonal variations of underlying surface physical variables are significant and closely related with each other. The seasonal variations of surface net shortwave radiation and sensible heat flux are significant and both start to increase in January. Their annual maximum values appear in May and June. Net long wave radiation is also high in May but low during the summer. Latent heat flux starts to grow remarkably in January and reaches its annual maximum value in the summer. Heat is transferred from the ground surface to the atmosphere since March, and then from the atmosphere to soil in September. Snow starts melting since March and decreases from March to May. Precipitation and vegetation water content begin to increase significantly in February. Rainfall increases sharply in May and June, leading to the peak value of 1-cm soil moisture. Precipitation, vegetation water content, plant transpiration, and total evapotranspiration all reach their highest values in July and August. During this time, the 1-cm soil moisture content is low but reaches its second peak in September. In October, with the underlying surface temperature turning cold, snow cover increases and 1-cm soil moisture decreases.