Based on single factor experiments,the adsorption of Cr⁶⁺ on fulvic acid(FA) from the soil was optimized by a combination design of quadratic regression and orthogonal rotation.The quadratic orthogonal regression model of potential removal rate of Cr⁶⁺(y) as function of four variables including FA density(x1),pH(x2),reaction time(x3) and reaction temperature(x4) was established.As implied by the model,the rate(y) reaches its peak of 78.27%with FA density of 2.11 g/L,pH value of 5.65,reaction time of 8.8 h and reaction temperature of 23.8 ℃.This model prediction was also consistently confirmed by experiment results.