Abstract: The pore size distribution at different temperatures and laterally spatial locations during pyrolysis was investigated by mercury intrusion method coupling with SEM analysis. A vertical furnace with the diameter of 150mm and the height of 300mm was used to simulate the coking process. The results show that there are a lot of macropore and mesopore existed in semicoke. A regular variation of porosity and specific surface area is observed with coking temperature and spatial location. At the same coking temperature, the porosity and specific surface area firstly decrease and then increase from the brim to the center of coke bed. The porosity decreases with the increase of the coking temperature, but increases after 900℃. The specific surface area reaches the minimum value at 900℃, and then rapidly increases with the increasing of temperature. The pores with the diameter of >5.0μm dominate all the pore structures. The cumulative pore volume with the pore diameter of <0.4μm、0.4μm~5.0μm and >5.0μm reaches 10 %、20 % and 70 %, respectively, and the distribution peak lies in the pore size between 60μm and 150μm. The SEM analysis results also show that the rich macropore is existed in the semicoke and the larger pore diameter is observed in the center and brim of the coke cake.