Abstract: The formula of inductive magneticmoment of the ferromagnetic shield was derived for the thickness design of shield used for highprecision magnetic detection. And then the bestthickness of the shield was defined to establish the bestthickness model which is verified by an elaborated experiment. The results show that the magnetic leakage of the magnetic source in the shield decreases with the increase in the thickness which leads to the additional interference. The slope of magnetic leakage decreases, meanwhile the slope of the additional interference increases. The bestthickness model was validated by using the experimental results.