NOVELTY - A beta -crystal nitroguanidine is prepared by (A) preparation of nitroguanidine as raw materials, (B) nitroguanidine synthesis process, (C) preparation nitroguanidine white crystal, (D) preparation of acid guanidine, (E) nitroguanidine washing process, and (F) nitroguanidine drying process. The step (A) comprises providing 60-90 mass% concentrated nitric acid, powdered guanidine nitrate, 20-40 mass% dilute nitric acid and 2-5 mass% sodium carbonate solution. The step (F) heating wet nitroguanidine at 60 degrees C and drying for 6 hours and obtaining 99% pure beta -crystal nitroguanidine.    USE - Method for preparation of beta -crystal nitroguanidine (claimed).    ADVANTAGE - The method avoids unqualified acidity and purity of product, saves energy consumption and avoids secondary pollution.    DETAILED DESCRIPTION - ~B-crystal nitroguanidine is prepared by (A) preparation of nitroguanidine as raw materials, (B) nitroguanidine synthesis process, (C) preparation of nitroguanidine white crystal, (D) preparation of acid guanidine, (E) nitroguanidine washing process, and (F) nitroguanidine drying process. The step (A) comprises providing 60-90 mass% concentrated nitric acid, powdered guanidine nitrate, 20-40 mass% dilute nitric acid and 2-5 mass% sodium carbonate solution. The step (B) comprises adjusting lower-temperature bath to 10 degrees C, adding 90 mL concentrated nitric acid to 250 mL four-opening flask, starting stirrer where stirring paddle is made of PTFE, adjusting rotating speed to 270-350 revolutions/minute, adding 30 g guanidine, and controlling feeding speed at temperature of less than or equal to 15 degrees C; after finishing feeding lower-temperature bath temperature is adjusted to 45 degrees C and reacting at 43 degrees C for 30 minutes; and after finishing reaction, cooling nitroguanidine solution to - 3 degrees C to - 7 degrees C. The step (C) comprises in the reaction solution of nitroguanidine, dropping 360-450 mL dilute nitric acid, controlling crystallization temperature of reaction system at - 3 degrees C to - 71 degrees C, controlling dripping speed of 0.5-5 mL/minute, and stirring at 600-800 revolutions/minute (rpm) to obtain nitroguanidine white crystal. The step (D) comprises continuously stirring at speed of 600-800 rpm, controlling temperature at - 3 degrees C to - 7 degrees C, filtering and separating waste acid to obtain acid guanidine. The step (E) comprises adding obtained acid nitroguanidine, into 250 mL four-opening flask at room temperature with mechanical stirring, water washing, adding 135 mL water and stirring for 15 minutes, and stirring at 900-1200 rpm; washing after filtering and separating, adding filter product to 250 mL four-mouth flask, using same method for re-washing, stirring and washing 3 times; and washing with 5% sodium carbonate solution, filtering and separating, and obtaining wet nitroguanidine. The step (F) heating wet nitroguanidine at 60 degrees C and drying for 6 hours and obtaining 99% pure beta -crystal nitroguanidine.