Abstract: Study of a series of strong-reductivity humic coals of 0.55 to 1.0 in rank by coal petrologic technique reveals that they contain high proportion of vitrinite-liptinite transition maceral.The properties of this transition maceral is that it has relatively lower reflectance and stronger fluorescence,and higher oil potential than normal desmocollinite.Based on its microcharactors,this transition maceral may be devided into two maceral types——intertexture type and swelling type.This transition macerals is the orther form of expression of fluorecent desmocollinite,and one of the principal parent substance of strong-reductivity humic coal-formed oil.