Abstract: Based on mecury injection experiments a otal of 10 coal samples cllcted from main coal seams in Bide-santang Basin were studied on difrent scales n orer to qu antitatively descibe the complexityof pore stucture using the fractal dimension.The relationship between fractal dinension and physical properies ofcal reservoir was claified.The resut showed that factal of coal resevir in ths area could be divided into mac.opore fractal between coal matrix paricles ,ranstion pore fracal in cal matrix paricles.,and they had igher frctal dimension. The thrd kind was micropore and minipore fractal ncoal matix paricles,which was lower in fractal limension. Thecomplex degree of these three pore structures were ranstiton pore>macropore>micropore and minipore.The negative corelation was existed between pore fractaldinension and porcosity volume frction in difrent scaes.Mfacopore an transtion pore fractaldfimension showed hghlovw-high change rule with metamorphic grade irimite ash,whielow-highn-low change rule with inertnire he positive relationship with moisture and mercury withdra wal eficiency existec,while negativerelationshio with mean pore size and porosity .Micropore and minipore fracteal dinension showed low-high-ow change rue with metamophic grade and vitrinte wie hgh-ow-high change rule with inetinite and ash.The negaive relationship with moisture and mercury withdrawal eficsency exsted,whiepostive relationshio with meanpore size and porosity.