Effects of application rate and N:K:Mg ratio of the fertilizer on yield of ball cabbage were studied through experiment of quadratic orthogonal regression design. A relative function model was thus obtained. With the aid of computer, the model was optimized and parsed, showing that when the application rate of urea, K₂SO₄ and MgSO₄ was 465.19, 97.38 and 28.48kg/hm², respectively, the yield of ball cabbage was the highest (111.89 t/hm²), but the optimum application rate of urea, K₂SO₄ and MgSO₄ was 460.37, 96.14 and 28.36kg/hm², respectively, when the cost of fertilization would be 818.98 yuan/hm², the profit 42,895.59 yuan/hm² and the O/I 52.4:1.