Used Xinjiang Cole alkali bentonite as the raw material and added different proportions of Na2CO3,to study the effection of adding modification to colloid valency,expansion volume and pH of bentonite.In addition,considered that non-saturated hydraulic properties of compacted bentonite is significant to the evaluation of backfill and buffer material properties.So the author used pressure plate extractors to measure soil-water characteristic curve of the original bentonite and Na2CO3 modified bentonite,to analyze the relationship between matrix suction and volumetric water content.The experimental results showed that adding Na2CO3 modification could increase bentonite’s valency,expansion volume,pH and transform calcium montmorillonite to sodium montmorillonite successfully.The influence of the pH of Cole alkali bentonite meets the requirements of geological repository to backfill and buffer material.Water-holding capacity of modified bentonite is significantly lager than the original bentonite.