Abstract: The microstructure features of voids in cement-bentonite slurrie are explored by mercury intrusion porosimetry(MIP) test.The research contributes to the knowledge of the strength and anti-seepage properties of cement-bentonite slurries from each affecting factor and mechanism.The study results show that the void structure characteristics,such as the total void volume,the probable void size,void distribution and critical void diameter,of the slurries are in direct relation to the amount of bentonite and cement in the mixture.The bigger voids of cement-bentonite slurries ought to be mainly composed of the cement hydration products.And the bentonite after hydration containing tiny pores will fill in part of big voids in the hardened paste.