A preparation method of improved sintered neodymium-iron-boron, Nd-Fe-B, casting strips, comprising the following steps: step 1. preparing nucleation assisted alloy particles used for sintered Nd-Fe-B casting strips 1.1) weighing the following nucleation assisted alloy particle elements: 26.68-28 wt% of Pr-Nd, 70-72.5 wt% of Fe and 0.90-1 wt% of B, wherein a Pr element in two elements of Pr-Nd accounts for 0-30 wt%; and obtaining alloy strips with proportion of ingredient atoms close to that of (Pr-Nd) 2 Fe 14 B through conventional compounding, smelting and pouring; and 1.2) crushing the alloy strips into particles with diameter of 1-10mm, to serve as the nucleation assisted alloy particles used for the sintered Nd-Fe-B casting strips; wherein, in the step 1.1, an Fe element in the nucleation assisted alloy particles can be replaced with part of a Co element, and the Co element accounts for 0-5 wt% in the nucleation assisted alloy particles; step 2. preparing Nd-Fe-B alloy casting strips 2.1) designing the proportion of ingredients of intermediate materials according to the marks of the Nd-Fe-B casting strips expected to be prepared and addition quantity of the nucleation assisted alloy particles, wherein the addition quantity of the nucleation assisted alloy particles is 3-6 wt% of weight; and 2.2) after being proportioned, smelting the intermediate materials into molten steel according to a conventional sintered Nd-Fe-B smelting technology, and conducting refining; adding the nucleation assisted alloy particles after the intermediate materials are melted and smelted for 10-20 minutes, and conducting smelting for 3-15 minutes under the condition that power is reduced by 150-250 kW in respect of the smelting power for the intermediate material, followed by pouring, thereby obtaining the Nd-Fe-B alloy casting strips. step 1. preparing nucleation assisted alloy particles used for sintered Nd-Fe-B casting strips 1.1) weighing the following nucleation assisted alloy particle elements: 26.68-28 wt% of Pr-Nd, 70-72.5 wt% of Fe and 0.90-1 wt% of B, wherein a Pr element in two elements of Pr-Nd accounts for 0-30 wt%; and obtaining alloy strips with proportion of ingredient atoms close to that of (Pr-Nd) 2 Fe 14 B through conventional compounding, smelting and pouring; and 1.2) crushing the alloy strips into particles with diameter of 1-10mm, to serve as the nucleation assisted alloy particles used for the sintered Nd-Fe-B casting strips; wherein, in the step 1.1, an Fe element in the nucleation assisted alloy particles can be replaced with part of a Co element, and the Co element accounts for 0-5 wt% in the nucleation assisted alloy particles; 1.1) weighing the following nucleation assisted alloy particle elements: 26.68-28 wt% of Pr-Nd, 70-72.5 wt% of Fe and 0.90-1 wt% of B, wherein a Pr element in two elements of Pr-Nd accounts for 0-30 wt%; and obtaining alloy strips with proportion of ingredient atoms close to that of (Pr-Nd) 2 Fe 14 B through conventional compounding, smelting and pouring; and 1.2) crushing the alloy strips into particles with diameter of 1-10mm, to serve as the nucleation assisted alloy particles used for the sintered Nd-Fe-B casting strips; wherein, in the step 1.1, an Fe element in the nucleation assisted alloy particles can be replaced with part of a Co element, and the Co element accounts for 0-5 wt% in the nucleation assisted alloy particles; step 2. preparing Nd-Fe-B alloy casting strips 2.1) designing the proportion of ingredients of intermediate materials according to the marks of the Nd-Fe-B casting strips expected to be prepared and addition quantity of the nucleation assisted alloy particles, wherein the addition quantity of the nucleation assisted alloy particles is 3-6 wt% of weight; and 2.2) after being proportioned, smelting the intermediate materials into molten steel according to a conventional sintered Nd-Fe-B smelting technology, and conducting refining; adding the nucleation assisted alloy particles after the intermediate materials are melted and smelted for 10-20 minutes, and conducting smelting for 3-15 minutes under the condition that power is reduced by 150-250 kW in respect of the smelting power for the intermediate material, followed by pouring, thereby obtaining the Nd-Fe-B alloy casting strips. 2.1) designing the proportion of ingredients of intermediate materials according to the marks of the Nd-Fe-B casting strips expected to be prepared and addition quantity of the nucleation assisted alloy particles, wherein the addition quantity of the nucleation assisted alloy particles is 3-6 wt% of weight; and 2.2) after being proportioned, smelting the intermediate materials into molten steel according to a conventional sintered Nd-Fe-B smelting technology, and conducting refining; adding the nucleation assisted alloy particles after the intermediate materials are melted and smelted for 10-20 minutes, and conducting smelting for 3-15 minutes under the condition that power is reduced by 150-250 kW in respect of the smelting power for the intermediate material, followed by pouring, thereby obtaining the Nd-Fe-B alloy casting strips.