Abstract: X-Ray Fluorescence (XRF) analysis is an effective assistant means in testing of gems. Without standard samples, the major elements of gems which the atomic number is over 22 are tested by portable X-ray fluorescence spectrometer in this paper. The spectrogram tested by the instrument is fitted with the PeakFit software and the major elements are analysed qualitatively or semiquantitatively. The application and method in testing of gems are introduced such as natural gems, treated gems, man-mades stones and imitation gemstones, combined with the gemmological characteristics for denominating samples. The results show that the instrument has many advantages. They are quick speed of the testing, nondestructive testing, wide detection range and reliable results.The method is an effective assistant method in the testing of gems especially when some conventional testing cannot be used.