The invention provides a method for improving the nitrogen yield of ferrosilicon nitride. Based on the steelmaking processes of molten iron pretreatment, converter blowing, RH vacuum treatment and continuous casting, a ferrosilicon nitride core-spun yarn is fed before converter tapping is finished or before refining, and the molten iron is stirred by using nitrogen or argon at the same time; the molten iron condition when the ferrosilicon nitride core-spun yarn is fed is that the oxygen activity is less than 50ppm; and the ferrosilicon nitride core-spun yarn consists of a wrapping and core powder; the core powder is prepared from the ferrosilicon nitride and has the granularity of less than or equal to 0.5mm, particles with the granularity of more than 0.5mm account for no more than 10 percent of all particles, and the diameter of the core-spun yarn is 9 to 16mm. Through the method, the nitrogen yield of the ferrosilicon nitride is improved to over 75 percent from below 30 percent, the fluctuation of the yield is small, and the repeatability is high; and the nitrogen content of the molten iron can be accurately controlled in the subsequent refining process.