Using the independently designed high pressure sample preparation mold and high pressure sample preparation technology (patent number: 201310125772.5), studies on the high pressure pressed various geological samples such as rocks, soils and stream sediments were first described in the present paper. It is the first experiment conducted in this field with significant achievements obtained. Without any binder, various types of geological powder samples can be pelleted well using 1600KN high pressure method. Such pellet has the characteristics of dense, flat, smooth and shiny surface, no cracks, no delamination, and no powder dropping. The study provides a new and contamination-free approach to sample preparation of X-ray fluorescence spectrum analysis. The comparison study conducted between the same samples pelleted under the low pressure (400 kN) and high pressure (1 600 kN) showed that using the high pressure the element peak to background ratios, and sensitivities are significantly improved, the detection limits are lowed, and the accuracies, the precisions and sample preparation repeatability are greatly improved. The Si FWHM became wider for the high pressure (1 600 kN) pellet than the same sample pelleted under the lower pressure (400 kN). The further SEM observation revealed that variation of Si spectrum shape may be caused by that the silica crystal lattices are destroyed and the particle size becomes smaller by using the high pressure pelleting techniques. So the particle size and mineral effects are also effectively reduced and the precisions and accuracies of the analytical method are improved.