As a macroscopic coherent state formed by the condensation of electron-hole bound pairs-excitons,excitonic insulators still lack clear experimental evidence for their realization in actual materials since the commencement of theoretical research on them.Therefore,the theoretical exploration of more novel systems and the search for more candidate materials that can realize excitonic insulators are still hot topics in current research.In this paper,we systematically investigated the excitonic insulators generated from parent materials such as semiconductors,normal semimetals,and Dirac semimetals.Using impurities as probes,utilizing mean-field theory as well as the T-matrix approximation,we found that nonmagnetic impurities have pair-breaking effect in excitonic insulators,inducing the generation of bound states.For excitonic insulators based on parent materials of normal semimetals and semiconductors,the intra-band and inter-band impurity scattering strength has a significant modulation effect on the numerical value and number of bound state energy levels.In contrast,the bound state energy levels in excitonic insulations with Dirac semimetals as the parent materials are hardly affected by impurity scattering.In addition,the impurity induced bound states show very different energy characteristics in the three different excitonic insulators.Lower energy inter-gap bound states can be produced in the excitonic insulators generated from normal semimetals than semiconductors,while the excitonic insulators generated from the Dirac semimetals have bound states tightly situated near the band-gap edge.