The invention belongs to the field of the preparation of polyamide fibers. In the technical scheme, the invention comprises the following steps of: extruding an ultrahigh molecular weight polyamide 6 spinning solution which contains calcium chloride serving as a complexing agent from a spinning pack, introducing the spinning solution into a coagulating bath composed of tetrachloroethane and trichloromethane for quenching into a primary gelatin silk, stretching the primary gelatin silk at room temperature, decomplexing in a mixed solution of ethanol and water, then heat stretching, and finally heat setting to obtain an ultrahigh molecular weight polyamide 6 fiber. In the invention, the stretching of the polyamide 6 fiber can be over eight times, the fiber maximum strength can reach 70.3GPa, and the breaking strength is over 0.4Gpa.