After the mineral dressing of iron ore from Bayan Obo ore, the content of scandium is up to 0.05% in tailings, which make it very valuable for utilization. A method for determine the trace scandium in the tailings and Niobium-rich slag with ICP-MS was established in this paper as a simple method with high sensitivity and accuracy. The working parameters of instrument, sample processing, the interference and eliminating method of coexisting elements were researched systemically. Cesium, thallium and rhodium were selected as the proper internal standard elements to overcome the non-mass spectrometry interference in the procedure of determination. The results of interference investigation showed that some elements in tailings, such as boron, silicon, calcium, zirconium and aluminum, were likely to cause mass spectrometry interference for the determination of scandium, but the concentration of boron was low(<100 μg·mL-1) in the sample that made it have not noticeable interference in the determination. In addition, smaller mass spectrometry interferences made by aluminum and calcium were negligible under the condition of determination. Most noticeably of all, zirconium and silicon mass interferences were more serious, zirconium would form a double charge (90Zr++) ion to interfere the 45Sc+, actually double-charged ions ionization yield was generally not high enough, the interference would be ignored at low concentration, if higher content of zirconium existed, the equation c′=0.021c(Zr)-0.55 was used to correct results. Moreover, high dissociation energy of silicon-oxygen bond and high related isotopic abundance made silicon oxides (28Si17O+, 29Si16O+) have higher stability, therefore the interference in the Bayan Obo ore tailings at measurement condition was more serious, and the formula c″=0.013c(Si)+0.019 can be used to correct results when silicon was not removed in the pretreatment. In summary, the mass spectrometry interferences to the scandium could be eliminated at determination of tailings. Four different sample pretreatment methods were studied and the result showed that sample determination results were consistent with the standard value and the recoveries of standard sample which were between 97%~99%; the silicon and boron mass spectrometry interferences was effectively overcame when used a mixed acids treatment method which contained Hydrochloric acid, hydrofluoric acid and sulfuric acid, besides it could cut down the measurement fluid salinity therefore so then reduced non-mass spectrometry interference. Standard and actual samples were determined and the results showed that the method, established in this paper to direct determination of scandium of the Bayan Obo metallurgical tailings by ICP-MS, was accurate and the relative standard deviation was less than 5%, and the method detection limit was 0.000 1%.