Taking a horizontal terrace on a slightly sloping land with a gradient less than 2° in northern Yangzhou, Jiangsu Province for example, spatial variability of soil moisture in the terrace was analyzed. Soil moisture of a terrace on the upper level is higher than that of the lower one, and soil moisture of the inner side is higher than that of the outside in the same terrace. Based on the distribution of soil moisture, an effective method named Kriging using trends as auxiliary information (KTAI) was proposed. The method taking into account the effects of both elevation of different terrace levels and different locations of the same level terrace on soil moisture, was used to interpolate the soil moisture in terraces. KTAI is useful for studying spatial variability of soil moisture in terraces and extending the application of geostatistics in spatial variability of soil moisture.