In the teaching of electromagnetism, it is often asked whether the electric displacement vector D is related to the polarization charge. In this paper, the relation between the electric displacement vector D and the polarization charge is further discussed based on the viewpoints and arguments presented in previous literatures. The results demonstrate that due to the constraint relationship between free charges and polarization charges, it is inaccurate to simplistically state that the electric displacement vector D is either related or unrelated to polarization charges. The “conditions under which D is independent of polarization charges” proposed in previous literature should be more appropriately termed as “conditions under which the distribution of polarization charges does not affect the original distribution of free charges”.