Abstract: Compared with the traditional ammonium acetate exchange method and calcium acetate exchange method to determine cation exchange capacity (CEC), hexamminecobalt trichloride method has obvious advantages in the analysis of large quantities of samples. However, the application scope of this method is limited, and the detection results of neutral and alkaline samples are good, but the detection results of acidic samples are as low as 50%. In order to solve these problems, the pH was adjusted to alkaline with 2mol/L sodium hydroxide solution, the CEC value of the sample was significantly improved, and the determination results of both acidic and alkaline samples reached the range of standard values. By drawing the pH adjustment curve, the volume of 2mol/L sodium hydroxide solution was obtained in soil samples with different pH ranges, so as to adjust the pH value of unknown samples and realize the accurate determination of CEC. On the basis of the original method, the pH of the sample was adjusted to alkalinity, and the precision of the optimized method ranged from 1.02% to 3.82% (n=6). After optimization, the application scope of the method is expanded, the precision and accuracy are improved, and the detection efficiency of a large number of samples is effectively improved.