Reversely switched dynistor (RSD) is a semiconductor switch which is suitable to be used in pulsed power systems. In many trigger circuits of RSD, a magnetic switch is usually needed. In this study, the saturated inductance of the magnetic switch is simulated. In addition, the relative permeability of the magnetic switch in the forward saturation process is measured. Based on the experimental results, if H is in the range of 1000 A/m to 2000 A/m, the relative permeability should be set between 4 and 5.5. If H is in the range of 2000 A/m to 5000 A/m, the relative permeability should be set between 3 and 4.5. However, at the H of tens of kA/m, the inductance of the magnetic switch can be calculated at relative permeability is 1.