The invention discloses a nylon false-twisted yarn and a preparation method thereof. The false-twisted yarn is composed of melting sections and fluffy sections in an alternating mode, the total length of the melting sections accounts for 20%-80% of the total length of the false-twisted yarn, the length uniformity of the melting sections and the fluffy sections is 80% or above, the melting point of the false-twisted yarn ranges from 150 DEG C to 200 DEG C, and the breaking strength ranges from 3.5 cN/dtex to 5.5 cN/dtex. The nylon false-twisted yarn disclosed by the invention can be used for preparing hemp fabrics with different elastic styles by nylon fibers which are uniformly fused and high in strength.