Based on insitu observation and analysis in laboratory, mechanism of saltaccumulation in sodic saline under shallow groundwater level was explored Results show that within the study plot, 35×35m² in area, varying only 60 cm in altitude, existed four types of soils i.e. sodic saline meadow soil, shallow columnar sodic alkaline soil, white crust sodic alkaline soil and median-columnar sodic alkaline soil. Sodic saline meadow soil was distributed in depressons, and almost free of alkaline layer; white crust alkaline soil and mediancolumnar sodic alkaline soils on micro slopes and high flatland. An alkaline layer was found in 15~30 cm in depth in high flatland, with ESP (exchangeable sodium percent) being 70%. On micro slopes, ESP of soil in the surface layer was the highest, up to 75%. Groundwater table (initial level) demonstrated a three-dimension pattern, being concave in depression, thus forming a difference of 1 m in water table between depression and high flatland, which was basically leveled off within 24 hours. Variation of groundwater table in the freezing period was found to be somewhat related to formation and development of frozen soil. Groundwater table was gradually lowered during the freezing period, as a result of some groundwater moving into the frozen layer, leading to a higher moisture content therein. Soil moisture content in the surface layer of saline meadow soil increased from 20% up to 50% (over-saturated), during the period, demonstrating a significant increasing rate (p<0.05), however, it did not change much in the frozen layer of sodic alkaline soil. In the thawing period, salinity content in the surface layer of sodic alkaline soil increased quickly, especially in white crust sodic alkaline soil, by about 80%, whereas insignificant change was observed in the surface layer of saline meadow soil.