Abstract: According to the problem of the reservir falure and the borehole wall instability occured in thea rling proc.ess of the pore and crack coal and rock gasreservoir with loaw ressure c.ricient a micro-analysis and the experiment studlycomined method was appied to conduct the research and development on the drlng fuid system with the physical and chemical coodinative depressin fiterloss perormances.An APl water ossfest was conducted on thea iling fuid prepared with he ulr-ine iner materials and chemicaladditives and the means of the scanning electron microscopy analysis were appied to the mophology analysis on the mud cakes formed. Thec ling fuid optinized formulaon with the physical and chemical coordinative depressing fiterloss peromances was researched and developed withorhogonal experiment.The means of the sca ming electron microscopy analysi were applied to the mophology analysis and the perfomance evaluation on the mud cakes. APl experiment and scanning electron microscopy analysi revealed that hollow glass micosphere inreased th fiterloss of basec mud due to is paticsles fomina space structure with developed micron pores by bridging in the mud cake.Th flfr loss rapilyinreased fom 24 m L to 50 m L with the increasing of an -lia doses.due to nan silia forming a oose spatial structure which had the big porosty, Htowever.th fitfr loss o firate reducers decreased fom 24 m L to 10 m L by forminga smoth and compact mud cake. Finaly.the illin fuid formulation withufrafine iner material was optimized by orthogondlfest. The studly achievements would haveimportant sigrificances to reveal the interaction mechanism between the ultra fine iner material and the clay mineral and the fitate reducer and to the rapid arllin of the coal and rock reservoir with low pressure coefficient pore and cracks.