The invention discloses a preparation method of a nuclear power station control rod drive mechanism's detachable joint, comprising the following steps: 1) selecting raw materials and carrying out vacuum melting to obtain molten steel; 2) pouring an electrode by the use of the molten steel; 3) carrying out electroslag remelting of the electrode to obtain an electroslag remelting ingot, wherein the electroslag remelting ingot contains, by weight, 0.080-0.140% of C, Si being less than or equal to 0.50%, Mn being less than or equal to 0.80%, S being less than or equal to 0.020%, P being less than or equal to 0.030%, 0.50-1.00% of Ni, 11.50-13.00% of Cr, Co being less than or equal to 0.10%, Al being less than or equal to 0.050%, Mo being less than or equal to 0.60% and the balance Fe; 4) carrying out annealing treatment on the electroslag remelting ingot and then carrying out forging-cogging; and 5) carrying out annealing treatment on billets, carrying out hot rolling on round steel, carrying out quenching and tempering heat treatment on the round steel and carrying out ultrasonic flaw detection to obtain the nuclear power station control rod drive mechanism's detachable joint. By optimization of chemical composition and technology, the CRDM detachable joint obtained by the preparation method can safely operate under service conditions, a clutch part at an end portion operates within an elastic range and plastic deformation will not happen. Life meets design standards and national standard requirements of CRDM, and manufacturing nationalization of CRDM is realized.