This paper analyses and studies control of nitrogen on Al- killed steel using the methods of production experiment in the flow of molten iron pretreatment - 180t converter - LF refining – continuous caster. Results show that adding aluminum final deoxidization should be divided into two steps: Firstly, putting some aluminum into molten steel after adding alloy in the process of tapping of molten steel, making the [O] reduce to 6 ~ 7ppm. Secondly, adding aluminum wire in LF-refining making [O] and [N] reach the required values. LF-refining should try to shorten operating time and original mission ought to be finished ahead. Desulfurization should be completed in the flow of molten iron pretreatment and the tapping of molten steel. Process of removal inclusions should be accomplished by adding slag during tapping of molten steel and blowing-mixing. LF-refining has scarcely any slagging task, it only needs to complete adjustment ingredient task. Alloy and carburant which contains extremely low nitrogen should be choosed, so that nitrogen in molten steel can be steadily controled below 30ppm.