The adsorption is a physico-chemical process in soil and aqueous environment. Precise determination of adsorption equilibrium isotherms of pollutants helps to understand their potential damages to environment. In this work, how solution pH and the Solid/Liquid (S/L) phase ratio affect the precision degree of results as to pollutants on adsorbents were investigated by calculating the relative deviation (R.D.) of the amount of adsorption (q e). Results show that the R.D. of q e might increases adversely with solution pH, and both pH and the concentrations of pollutants (C e) should be carefully measured. The degree of the influence of the S/L phase ratio is greatly determined by the adsorption coefficient K d.