NOVELTY - High-purity seed circulating injection of re-crystallized methyclothiazide comprises: (i) adding methyclothiazide and crystallizing solvent into a crystallization vessel, heating under stirring and reflux condition, filtering hot solution and re-crystallizing to obtain seed preparation; and (ii) adding methyclothiazide raw material and seeds into the crystallization vessel, adding crystallization solvent and re-crystallizing, filtering to obtain high-purity crystals and re-extracted seeds simultaneously and repeatedly extracting by injecting recycled seeds for 1-4 times for re-crystallization.    USE - The method is useful for high-purity seed circulating injection of re-crystallized methyclothiazide (claimed).    ADVANTAGE - The method: utilizes less crystallization solvent; and improves production efficiency and yield rate up to 10-30% with one-time re-crystallization.    DETAILED DESCRIPTION - High-purity seed circulating injection of re-crystallized methyclothiazide comprises: (i) adding methyclothiazide and 20-40 times volume crystallizing solvent into a crystallization vessel, heating for 30 minutes under stirring and reflux condition for complete dissolution, filtering hot solution, allowing it to stand for greater than or equal to 12 hours and re-crystallizing to obtain seed preparation, where the crystals produced in the process is high-purity methyclothiazide crystals which are filtered simultaneously during extracting seed; and (ii) adding methyclothiazide raw material and seeds into the crystallization vessel, adding 20-40 times volume crystallization solvent and re-crystallizing, filtering to obtain high-purity crystals and re-extracted seeds simultaneously and repeatedly extracting by injecting recycled seeds for 1-4 times for re-crystallization. An INDEPENDENT CLAIM is also included for re-crystallizing methyclothiazide in methanol, comprising re-crystallizing methyclothiazide raw material for 1-3 times, dividing re-crystallized material into 2-4 batches every time, where the feeding amount in each batch is 0.5-0.8 times, adding 20-40 times volume methanol, heating for 30 minutes under stirring and reflux condition for complete dissolution, cooling, adding activated carbon and heat refluxing for 30 minutes, filtering hot solution, allowing it to stand for 12 hours, drying the filter cake at 70 degrees C under reduced pressure, and using the filtrate as seed for next batch of re-crystallization; using re-crystallized 2, 3 and 4 sub-batches for re-crystallization by adding 20-40 times volume methanol to obtain re-crystallized product, mixing the product with first batch to obtain first re-crystallized product; and feeding 0.7 times 2-3 sub-batches for second re-crystallization to obtain secondary re-crystallization product, re-crystallization for third time to obtain third re-crystallization product.