A process preparation technology of sintered NdFeB magnets from NdFeB sludge. The method of the present invention comprises the following steps: water bath distillation of sludge, ultrasonic cleaning, calcium reduction and diffusion, ultrasonic rinsing in a magnetic field, drying, powders mixing and sintering: Water bath distillation of sludge: Distilled water was added into the sludge and stirred. Subsequently, water bath distillation with stepwise increasing temperature in vacuum was carried out until the internal liquid had evaporated to obtain the powders. The operation was repeated for 3 times; Ultrasonic cleaning for sludge: The distillation powders after step were washed for 3 times by acetone in an ultrasonic vessel, followed by cleaning by ethanol in the ultrasonic vessel. After removing the liquid, the wet powders were dried to get the pretreatment powders; Calcium reduction-diffusion: The pretreatment powders after step with appropriate amounts of Nd 2 O 3, FeB, and CaH 2 as the reactant, and CaO as a dispersant were used in the calcium reduction diffusion reaction; wherein the pretreatment powders after step were analyzed by x-ray fluorescence. Based on XRF results and calculations in accordance with RE 2 Fe 14 B stoichiometric ratio, Nd 2 O 3 was added to make sure that the amount of rare earth was 40 wt. % of the mixed powders of pretreatment powders, Nd 2 O 3 and FeB; FeB was added to make sure that the amount of B in mixed powders of pretreatment powders, Nd 2 O 3 and FeB was in excess 0-10 wt. % of that in the RE 2 Fe 14 B compound; The quantity of CaH 2 was 1.2-1.3 times as large as the mixed powders; The quantity of CaO was 50 wt. % of CaH 2, and wherein the reduction diffusion reaction condition was carried out at 1160-1240 °C for 60-150 min in inert gas; Rinsing and drying: The reducing product after step was grinded, ultrasonically rinsed in a glass container in a magnetic field, and then dried; Mixing powders and sintering: the resulting recycled NdFeB powders after step were milled down to 3-5 μm, doped by rare earth hydride nanoparticles of 10-20 wt. %, and mixed; subsequently pressed and aligned in a magnetic field to obtain the compact. The green compact was first dehydrogenated at 900-1000 °C for 30-180 min, and then sintered at 1050-1150 °C for 120-240 min, and finally annealed at 850-950 °C for 60-180 min and 450-550 °C for 60-180 min, respectively. The recycled sintered magnets were thus obtained. Water bath distillation of sludge: Distilled water was added into the sludge and stirred. Subsequently, water bath distillation with stepwise increasing temperature in vacuum was carried out until the internal liquid had evaporated to obtain the powders. The operation was repeated for 3 times; Ultrasonic cleaning for sludge: The distillation powders after step were washed for 3 times by acetone in an ultrasonic vessel, followed by cleaning by ethanol in the ultrasonic vessel. After removing the liquid, the wet powders were dried to get the pretreatment powders; Calcium reduction-diffusion: The pretreatment powders after step with appropriate amounts of Nd 2 O 3, FeB, and CaH 2 as the reactant, and CaO as a dispersant were used in the calcium reduction diffusion reaction; wherein the pretreatment powders after step were analyzed by x-ray fluorescence. Based on XRF results and calculations in accordance with RE 2 Fe 14 B stoichiometric ratio, Nd 2 O 3 was added to make sure that the amount of rare earth was 40 wt. % of the mixed powders of pretreatment powders, Nd 2 O 3 and FeB; FeB was added to make sure that the amount of B in mixed powders of pretreatment powders, Nd 2 O 3 and FeB was in excess 0-10 wt. % of that in the RE 2 Fe 14 B compound; The quantity of CaH 2 was 1.2-1.3 times as large as the mixed powders; The quantity of CaO was 50 wt. % of CaH 2, and wherein the reduction diffusion reaction condition was carried out at 1160-1240 °C for 60-150 min in inert gas; Rinsing and drying: The reducing product after step was grinded, ultrasonically rinsed in a glass container in a magnetic field, and then dried; Mixing powders and sintering: the resulting recycled NdFeB powders after step were milled down to 3-5 μm, doped by rare earth hydride nanoparticles of 10-20 wt. %, and mixed; subsequently pressed and aligned in a magnetic field to obtain the compact. The green compact was first dehydrogenated at 900-1000 °C for 30-180 min, and then sintered at 1050-1150 °C for 120-240 min, and finally annealed at 850-950 °C for 60-180 min and 450-550 °C for 60-180 min, respectively. The recycled sintered magnets were thus obtained.