The invention discloses a method for recovering phosphorus in a crystallization way from semiconductor industrial waste water. Main operation steps of the method are as follows: adding magnesium source to semiconductor industrial waste water; supplementing nitrogen source if necessary; controlling pH value of waste liquid; adjusting the molar ratio of magnesium salt: ammonia nitrogen: phosphate salt, blending the mixture for a certain time in a mechanical blending mode; continuously heating waste liquid in the initial phase of stirring; and keeping temperature constant after waste liquid reaches a certain temperature till the blending is over. After blending, waste liquid is statically placed and settled for a certain time; after static settling, liquid supernatant and crystallized precipitates are separated; and the crystallized precipitates can be recycled after being dried. By the process treatment, more than 90% of phosphorus in the semiconductor industrial waste water can be effectively recycled; the recycled product is dense and plump; the technology has the advantages of short response time, high product purity, simple process, simple and convenient operation, low cost and the like and has obvious environmental, economic and social benefits.