Abstract: In this article the Penning-type negative hydrogen ion source of 11 MeV compact cyclotron is studied. This ion source works in arc-mode. By changing the magnetic field strength, the impact of the magnetic field on ion sources work situation is analyzed. These issues are analyzed in the article: the mechanical properties of sustained discharge in the ion source, the impedance change of the ion source when the magnetic field varies, abnormal glow observed at the extraction slit. In this experiment, when hydrogen flow is stabled at 6 mL/min, changing the magnetic strength will influence Penning discharge. The result indicates that at strong magnetic field condition, the plasma conductivity almost does not change; but when the magnetic strength gets weak (less than 0.15 T), the plasma resistivity will increase rapidly, and there is a fierce discharge/glow of plasma brightening rapidly in this condition. Some inspiration in the design of PIG source are got from this experiment, and we are trying to analyze the probable microcosmic physics mechanism of this phenomenon in the discussion.