The invention discloses a preparing method of chymosin dry casein with ''curve draw'' as raw material to solve problems of single variety, lag process and unstable quality, which comprises the following steps: grinding; twice-protecting colour; dissolving; filtering; eccentric-defatting; pumping filter liquor into centrifuger with rotary speed at 7500r/min-8500r/min; proceeding twice eccentric defatting; setting the discharge at 500 l/h-1000l/h; adding into chymosin; making mass percent of the added quantity makes up 0.25-1.0% of raw material; washing; dewatering; pelleting through granulation machine with sieve cloth at 30-60 order; drying; placing wet dry casein in drier; drying; getting the product. This invention adopts twice protecting colour craft to improve quality of the product, which can reach the standard of high grade dry casein.