Rare earth elements, with their unique electronic structure and active chemical properties, are important additives in the metallurgical industry and play an important role in many fields. Not only can rare earth additives be used as deoxidizer and desulfurized to purify the molten steel, but also have metamorphism and alloying effects on the steel, which can improve the structure and performance of the steel materials. However, only with a certain range can the addition of rare earth elements in steel materials shows good properties. Although inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectrometry are usually used to detect rare earth elements in steel materials, which require sample digestion and tedious operations for a long test period. In this study, portable energy dispersive X-ray fluorescence spectrometry was used to realize the rapid detection of lanthanum and cerium in steel materials, and the whole weight of the instrument is less than 10 kg, which is convenient to test on-site. Compared with selecting L series lines for analysis and testing in the traditional portable instrument, a high-power X-ray tube is used to excite the K series spectral lines for rare earth elements, which can increase the intensity of analyzed peaks and avoid overlap interference of other common components in steel materials. The intensity and peak-to-background ratio were studied at different X-ray tube current and voltage when the measured time was set at 120s, and finally, the optimized parameters were chosen as 800 μA and 65 kV for irradiating samples. The calibration curves were drawn with reference materials, and the linear correlation coefficients of lanthanum and cerium were 0.999 2 and 0.998 8 respectively, after the correction of matrix effect by the intensity of the background. Reference samples of GBW01135 were chosen to calculate the detection limit and quantitation limit because both the content of La and Ce were of low content. Moreover,the detection limit of La and Ce was 0.001 1% and 0.000 5% respectively, and the quantitation limit was 0.003 8% and 0.001 6%, which satisfied the requirement of the actual test. The stability of the test was studied by 11 consecutive measurements for the sample of GBW01132a, and the relative standard deviation was 2.42% and 2.00% for La and Ce. Furthermore,the accuracy of the test results was also studied by testing multiple samples and comparing with reference values. The results showed that the relative error of the results were less than 20% except for one sample which was below the detection limit, and the relative error of more than 70% samples were less than 10%. The energy dispersive X-ray fluorescence spectrometry can realize the rapid detection of rare earth elements in steel materials, and the samples can be directly tested with simply polishing pretreatment, which is of certain significance for further research on the properties of steel materials.