MMT was swelled by alcohol and water, and then dispersed evenly in the caprolactam melt. Water and ethanol were removed by vacuum dewatering in casting process, and MMT/MCPA6 composite materials were produced by anionic ring opening polymerization in MMT interlayer. The structure of composite materials was characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and the performance was measured by mechanical property test, thermogravimetric analysis and differential scanning calorimetry. The results showed that MMT swelled by ethanol and water was totally exfoliated in MCPA6 matrix, and it could induce gamma crystal shape of MCPA6 and improved crystallinity. However, MMT destroyed the regularity of crystal, hindered the movement of MCPA6 molecular chain and reduced the crystallization rate. The nanoscale dispersed MMT reduced the toughness of the composites slightly, but the strength was greatly improved, the tensile strength increased by 46.2%, the bending strength increased by 26.2%, and the bending modulus increased by 23.9%. MMT dispersed in nano scale played the part of heat insulation, and a small amount of MMT improved the thermal decomposition temperature and carbon residual rate of MMT/MCPA6 nanocomposite materials. Vicat softening temperature of MMT/MCPA6 nanocomposite materials was enhanced to 230℃, and heat deflection temperature of MMT/MCPA6 nanocomposite materials increased to 114℃.