Chlorine is an important analyte in geo-chemical exploration analysis. X-ray fluorescence spectrometry is a key technical method for the determination of halogen elements. Many studies have shown that chlorine’s measured value in the same pellet increases or decreases with the increase of repeated determination times when chlorine is determined by X-ray fluorescence spectrometry. In this paper, new sample preparation technique-high pressure pressed pellet covered with polyester film, and chlorine determination in soil and sediment is proposed. Cl’s correlation coefficient was markedly improved, and the RMS was reduced from 0.009 63 (without film) to 0.001 98 (with film). The limit of detection of chlorine was improved from 30 μg·g-1 without film-coating to 21 μg·g-1 with film-coating. And with the new sample preparation, the chlorine remained constant or showed only minor changes in 10 subsequent analysis or 10 subsequent daily irradiation. The reason for the measured value of chlorine increases or moderate decreases with the increase of repeated measurements is explained from the point of view of pre- vacuum time and X-ray tube application power, drying sample and non-drying sample, forms of chlorine. A high-pressure pressed powder pellet covered with polyester film can circumvent chlorine diffusion with moisture to the surface of the sample or decomposition loss. The vacuum degree decreases obviously with the increase of pre-vacuum time and desorption, and the intensity of chlorine changes obviously. With the introduction of the high-pressure film-coating sampling, the change of vacuum degree was not obvious, and the value of chlorine was remained constant or showed only minor changes. The high-pressure sample preparation (1 600 kN) solves the difficulty of forming different types of geological samples. The high-pressure film-coated sample preparation technology completely eliminates the dust effect and is of great significance to the X-ray fluorescence spectrometer under irradiation. Chlorine could be better identified with the used pellet, and the standard pellet could be preserved for a long time.Also it avoided misspending of the reference materials.This method can accurately determine 32 components in soil and water sediment. The sample preparation method is also suitable for the elemental analysis of other difficult to form samples and their fluorescence intensity changes due to vacuum and long-time irradiation.