A method for preparing a Nd-Fe-B isotropic magnetic powder, comprising S1. smelting alloy smelting and refining ingredients under vacuum to obtain an alloy ingot, and crushing the alloy ingot to obtain an alloy block, wherein the smelting is conducted at a temperature of 1,350-1,450 °C, and the refining is conducted at a temperature of 1,335-1,430 °C and a pressure of 900-1,100 Pa in an inert gas atmosphere for 3-7 minutes; S2. rapidly quenching alloy solution melting the alloy block obtained in step S1 to obtain an alloy solution, rapidly quenching the alloy solution to form a Nd-Fe-B rapidly-quenched alloy plate; S3. crushing alloy plate crushing the Nd-Fe-B rapidly-quenched alloy plate obtained in step S2 to obtain a magnetic powder; and S4. crystallization heat treatment subjecting the magnetic powder obtained in step S3 to a crystallization heat treatment in an inert gas atmosphere, and cooling, to obtain the Nd-Fe-B isotropic magnetic powder; wherein rapidly quenching the alloy solution in S2 is conducted under conditions: charging argon gas through a vacuum ball valve, maintaining a charging rate of argon gas of 0.2-1.5 m 3 /min; adjusting a vacuum butterfly valve, and maintaining a pressure of 200-2,000 Pa; the inert gas in steps S1 and S4 is argon gas; and the ingredients consisted of the following ingredients, in percentages by weight, 26.2% of rare earth metals praseodymium and neodymium, 4.7% of boron iron, 0.2% of metal niobium, 2.0% of metal cobalt, and the balance of ingot iron; the rare earth metals praseodymium and neodymium have a purity of 99.9%, in which the oxygen content is less than 400 ppm and the nitrogen content is less than 60 ppm; the ingot iron has a carbon content of less than 400 ppm, and a silicon content of less than 1,500 ppm; the boron iron has a boron content of 20.2%; the metal niobium has a purity of 99.5%; the metal cobalt has a purity of 99.9%, in which the oxygen content is less than 500 ppm, and the nitrogen content is less than 70 ppm. S1. smelting alloy smelting and refining ingredients under vacuum to obtain an alloy ingot, and crushing the alloy ingot to obtain an alloy block, wherein the smelting is conducted at a temperature of 1,350-1,450 °C, and the refining is conducted at a temperature of 1,335-1,430 °C and a pressure of 900-1,100 Pa in an inert gas atmosphere for 3-7 minutes; smelting and refining ingredients under vacuum to obtain an alloy ingot, and crushing the alloy ingot to obtain an alloy block, wherein the smelting is conducted at a temperature of 1,350-1,450 °C, and the refining is conducted at a temperature of 1,335-1,430 °C and a pressure of 900-1,100 Pa in an inert gas atmosphere for 3-7 minutes; S2. rapidly quenching alloy solution melting the alloy block obtained in step S1 to obtain an alloy solution, rapidly quenching the alloy solution to form a Nd-Fe-B rapidly-quenched alloy plate; S3. crushing alloy plate crushing the Nd-Fe-B rapidly-quenched alloy plate obtained in step S2 to obtain a magnetic powder; and S4. crystallization heat treatment subjecting the magnetic powder obtained in step S3 to a crystallization heat treatment in an inert gas atmosphere, and cooling, to obtain the Nd-Fe-B isotropic magnetic powder; wherein rapidly quenching the alloy solution in S2 is conducted under conditions: charging argon gas through a vacuum ball valve, maintaining a charging rate of argon gas of 0.2-1.5 m 3 /min; adjusting a vacuum butterfly valve, and maintaining a pressure of 200-2,000 Pa; the inert gas in steps S1 and S4 is argon gas; and the ingredients consisted of the following ingredients, in percentages by weight, 26.2% of rare earth metals praseodymium and neodymium, 4.7% of boron iron, 0.2% of metal niobium, 2.0% of metal cobalt, and the balance of ingot iron; the rare earth metals praseodymium and neodymium have a purity of 99.9%, in which the oxygen content is less than 400 ppm and the nitrogen content is less than 60 ppm; the ingot iron has a carbon content of less than 400 ppm, and a silicon content of less than 1,500 ppm; the boron iron has a boron content of 20.2%; the metal niobium has a purity of 99.5%; the metal cobalt has a purity of 99.9%, in which the oxygen content is less than 500 ppm, and the nitrogen content is less than 70 ppm. subjecting the magnetic powder obtained in step S3 to a crystallization heat treatment in an inert gas atmosphere, and cooling, to obtain the Nd-Fe-B isotropic magnetic powder; wherein rapidly quenching the alloy solution in S2 is conducted under conditions: charging argon gas through a vacuum ball valve, maintaining a charging rate of argon gas of 0.2-1.5 m 3 /min; adjusting a vacuum butterfly valve, and maintaining a pressure of 200-2,000 Pa; the inert gas in steps S1 and S4 is argon gas; and the ingredients consisted of the following ingredients, in percentages by weight, 26.2% of rare earth metals praseodymium and neodymium, 4.7% of boron iron, 0.2% of metal niobium, 2.0% of metal cobalt, and the balance of ingot iron; the rare earth metals praseodymium and neodymium have a purity of 99.9%, in which the oxygen content is less than 400 ppm and the nitrogen content is less than 60 ppm; the ingot iron has a carbon content of less than 400 ppm, and a silicon content of less than 1,500 ppm; the boron iron has a boron content of 20.2%; the metal niobium has a purity of 99.5%; the metal cobalt has a purity of 99.9%, in which the oxygen content is less than 500 ppm, and the nitrogen content is less than 70 ppm.