A series of diallyl methyl alkyl ammonium bromide(CCx, X is alkyl’s chain length，represent 12，14，16 and 18 respectively) was synthesized via two step. Monomer was determined by element analysis，NMR，and FT-IR. Organic montmorillonite was prepared by sodium montmorillonite and CCx as intercalating agent. Montmorillonite modified with CCx (CCx-MMT) was indicated by XRD, FT-IR and thermogravimetric analysis (TGA).The XRD results showed that a series of CCx could intercalate into the clay interlayer. XRD and TGA results show that the d spacing of the CCx-MMT was deviated from the linear relationship with TGA organic composition. FT-IR results indicated that the water absorption on the surface of CCx-MMT was effectively restricted and the hydrophobic was increased dramatically. The variety peak intensity at 2924 and 2854cm−1 was consistent with content of organic fraction in CCx-MMT.