Electromagnetic isotope separator is the important machine for isotope enriching of which ion source is the critical part. In China, the only one yielding-type electromagnetic isotope separator, named EMIS-170, locates in China Institute of Atomic Energy. It has been playing important role in providing highly enriched stable isotopes for many applications domestically, and the ion source used is the Calutron ion source. This paper investigates the dependence of ion beam current and beam oscillation of the Calutron ion source on the magnetic field in the EMIS-170 experimentally. It is observed that the beam current has a nonlinear relationship with the magnetic field. It significantly increases from 15 mA to 29mA with the increase of the magnetic field at the range of 170 G~620 G and decreases slowly to 26.7 mA when the magnetic field increases to 950 G. This phenomenon is analyzed qualitatively from the view of the primary electron motions along the magnetic field and the ion diffusion across the magnetic field. It is found that the model could predict the relationship between magnetic field and ion beam. The fluctuation of the beam current is observed trivial at 340~390 G with frequencies of about 20 kHz and 400 kHz and almost disappears at 620 G~730 G. As the magnetic strength is larger than 730 G, the fluctuation becomes quite obvious with frequencies of about 40 kHz and 250 kHz.