Abstract The calutron ion source used in the electromagnetic isotope separators in the Institute of Atomic Energy, Academia Sinica, is briefly described. By improving the construction and configuration of the arc chamber and electrode system, the ion source can produce a more intensive ion beam, for example, 80 mA for rubidium and 92 mA for strontium. The ion beam quality is also discussed. Non-uniformity in the ion density distribution along the emission slit direction is very pronounced. But it does not cause any considerable decompensation of the beam space-charge. The curve of beam angular divergence as a function of beam current is more complex than the vee-shape reported previously by some authors. There is a peak on the curve for a certain ion current and the beam with such an angular divergence can usually be well focused.