Saline-alkali soil is widely distributed in cultivated land in China, which seriously restricts the development of modern agriculture and rural construction. The mass fraction of soluble salts (Ca2+, K+, Na+ and Mg2+) in the surface layer of saline soil can reach more than 0.1%~0.2%. The excessive concentration of ions in this soil can hinder the absorption of other ions and nutrients by plants and harm the growth of crops through osmosis, stress or ion poisoning. Therefore, saline-alkali land improvement is an important direction of modern agricultural research. Accurate and rapid measurement of water-soluble cationic Ca2+, K+, Na+ and Mg2+ in saline-alkali soil is one of the important foundations and key technical problems for soil improvement. The traditional analytical procedure is oscillating the saline-alkali soil in water for several hours and then taking the supernatant solution for direct determination by atomic absorption spectrometry. As the detection limit of the atomic absorption spectrophotometer is far lower than that of the sample to be tested, multiple dilutions are required in the test process, which increases the systematic error of the test and reduces the credibility of the experimental results. Therefore, in this paper the X-ray fluorescence spectrometer was used to determine the Ca, K, Na and Mg content of original saline-alkali soil sample and residual sample after a certain oscillation time, and then the difference was calculated to obtain the soluble Ca2+, K+, Na+ and Mg2+ content. The test results were compared with those determined by atomic absorption spectrometry. The pH, electrical conductivity and the content change characteristics of the main anions Cl-, SO2-4, HCO-3 and CO2-3 in saline-alkali soil were obtained to confirm the method. The results show that by the X-ray fluorescence spectrometry the soluble Ca2+, K+, Na+ and Mg2+ ion contents do not change much after respectively oscillation for 1 ~ 6 hours. Almost all soluble cations dissolve after oscillation for 1 hour. The measured results of X-ray fluorescence spectrometry are basically consistent with those of atomic absorption spectrometry. In addition, the reliability of X-ray fluorescence spectrometry can also be verified by the mutations in pH and conductivity of the sample after oscillation for 1 hour, and the content changes of main anions obtained by ion chromatography and double neutralization indicator method. The X-ray fluorescence spectrometry method for indirect analysis of high content water-soluble salt cations in saline-alkali soil has the advantages of simple operation, safety, reliability and high accuracy.