The invention relates to the field of nylon materials, and discloses a method for preparing functional nylon 6 fiber based on the melt direct spinning technology. The method comprises the steps that firstly, burdening is conducted, caprolactam, an end-capping reagent, water and a catalyst are heated and mixed, and a mixture is obtained; secondly, ring opening is conducted; thirdly, pre-polycondensation is conducted, and the pre-polycondensation reaction and devolatilization are conducted; fourthly, final polycondensation is conducted, and the final polycondensation reaction and devolatilization are conducted; and fifthly, devolatilization is conducted before spinning; and sixthly, spinning is conducted, and the functional nylon 6 fiber is obtained. In the first step, functional componentsare added, or before devolatilization before spinning in the fifth step, functional nylon master batches containing functional components are added. The method can be divided into two parallel schemes, the functional components can be directly added in the first step, or the functional nylon master batches containing functional components are added before devolatilization in the fifth step. According to the method, fusion direct spinning is directly conducted after the functional components are added, devolatilization is conducted during pre-polycondensation and final polycondensation, and theproblem about poor functional component scattering can be solved.