SM-30 magnetic susceptibility instrument is favored by more and more geophysical workers because of its lightweight portability and the fact that it can be used in the field rock and ore magnetic susceptibility rapid analysis. The author summarized its advantages such as lightweight and sensitivity and its disadvantage of relatively low measuring accuracy. British Minisep and MS2 magnetic susceptibility instrument as well as SM-30 magnetic susceptibility instrument were used to make a comparative test for 279 drilling rock ore samples. Although the magnetic susceptibility determination results by the three kinds of instruments show strong correlation, the SM-30 magnetic susceptibility instrument has the shortcoming of low measurement precision, which deserves due attention.