Abstract: There are many calcified wood in lower subinterval of lower Zhiluo formation(J₂z^1-1) in the northern mountains of Huangtianmiantu town of Dongsheng. This paper analyzed the sedimentary environment of calcified wood, and described its petrological and mineralogical characteristics. Combined with previous research works, we preliminarily summarized the cause of formation of calcified wood in this region. It is found that, firstly, there are two kinds of wood fossil in J₂z^1-1 formation of this district, respectively calcified wood and carbonized-calcified wood, and they occurred in the scouring surface between BA and CVS as well as CCH; secondly, the mineral composition of calcified wood are mostly megacrystcalcite and very little carbonaceous fragments, but in carbonized-calcified wood the carbon content is higher and the calcite inside are microlite; thirdly, the genesis of calcified wood is that the underground water with Ca²⁺and CO₃^2- flowed into the pore of tree trunk and the calcite crystallized in it. It is considered that Ca²⁺ is derived from anorthosite erosion, and CO₃^2- probably comes from UO₂(CO₃)₃^2-.