Abstract: A single factor experiment was conducted to optimize the adsorption of soil Cr(Ⅵ) in soil by humic acid using a quadratic regression orthogonal rotation combination design. The quadratic orthogonal regression model of removal rate of Cr(Ⅵ) in soil(y) to four factors of humic acid (HA) dosage (x1), pH(x2), reaction time (x3) and reaction temperature(x4) was established as: Y=60.27012-2.22158X1+2.92002X3-4.29138X21-2.53068X22-2.00566X24-2.35375X1X2+3.68250X1X3-1.99875X1X4-1.99875X2X3+3.68250X2X4-2.35375X3X4. The optimal condition for Cr removal based on the model was: HA 1.86 g/L, pH 5.5, reaction time 8.56 h and reaction temperature 25.22℃. Under this condition, the y reached the maximum (80.0%), which was coincided with our experimental result.