The invention relates to the field of ferrous metallurgy, in particular to a method for accurately controlling the nitrogen content of high-nitrogen silicon-containing low-alloy steel at low cost. According to the method, nitrogen instead of Ar is bottom blown throughout smelting of a converter, and when the bottom blowing effect of the converter is poor, a converter blowing process of blowing nitrogen to molten steel by an oxygen lance is adopted in the post-stirring stage; aluminum and iron are pre-arranged at the bottom of a ladle before tapping, nitrogen is blown into the ladle instead ofadding nitrogen-containing alloy to increase nitrogen during tapping, and alloy is added to fix nitrogen during tapping; after tapping, bottom blowing of nitrogen is continued to supply nitrogen to the molten steel to ensure that the content of nitrogen in the molten steel before entering vacuum refining is larger than 80 ppm; in the vacuum process, accurate nitrogen increase is achieved by controlling nitrogen circulation time, accurate nitrogen removal technology is achieved by switching Ar in the high vacuum degree before the end of the treatment, and the content of nitrogen in the molten steel is accurately controlled. The method is convenient to operate and has obvious cost reduction effect, and is suitable for popularization and application in other converter vacuum production lines.