The invention relates to a preparation method for an organic amine-modified montmorillonite/polyamide nano composite material. The preparation method includes a step of adding a polyamide monomer, the organic amine-modified montmorillonite and pure water into a reaction kettle to prepare the nano composite material. In the process of preparing the polyamide through in-situ hydrolytic ring-opening polymerization, organic amine-modified montmorillonite is added so that the mechanical performance of the polyamide is improved. The nano composite material with the organic amine-modified montmorillonite, when being compared with other nano composite materials with montmorillonite or nano additives, has better improvement on mechanical performance and thermal stability, and also is improved in anti-wetting property. The preparation method is free of pre-dispersion or addition of a pre-dispersing device and can be used for preparing the organic amine-modified montmorillonite/polyamide nano composite material directly through a one-step method in a reaction kettle, thereby reducing production cost and further improving performance of the material.