Abstract: In the research area of the CT digital coal petrography, the selection of gray threshold directly affects the accuracy of spatial structure remodeling. To allow the pores and fissures space remodeling data to more accurately represent the real structure and improve the reliability of research on microscopic seepage of coal rock, the mapping relation between the CT digital coal rock porosity and gray threshold is established. Also, the distribution rule of gray threshold is adopted to conduct a quantitative analysis of the development features of pore, fissure and matrix. The Bi-PTI (Biphasic Pore Threshold Inversion) model is established for the identification of pore and fissure structures. The value inversion of the optimal gray threshold of pore and fissure based on the CT scanning data of metamorphic coal, and the comparison of porosity obtained with the model against the mercury injection test value are conducted. On the basis of the optimal gray threshold inversion results, the spatial structure of pore and fissure is remodeled and compared with the Otsu model through the parameters of spatial structure and topological structure. Research results indicate that the porosity based on the CT digital coal petrography is in asymmetrical S-shaped distribution as the threshold value increases, with the features of exponential increase and logarithmic climb at different sections. The Bi-PTI model can fairly reflect the mapping relation between porosity and gray threshold, and represent the development features of pore, fissure and matrix. The porosity calculated through the Otsu model is as high as over 70%, the porosity calculated by the MP-Otsu model is greatly affected by the mineral content while that calculated with the Bi-PTI model ranges from 0.40% to 16.22%, more close to the mercury injection test data. The Otsu model is most likely to neglect the topological structure with partial pores and fissures. The MP-Otsu model is not effective for constructing the topology of coal samples with low mineral content, while the Bi-PTI model can better identify the topological features in the locations of the defect and faithfully restore the pore throat abundance and connectivity in the pore and fissure topology.