The reservoir characteristics, diagenesis and diagenetic evolvement history of Carboniferous in Bayehot Basin were discussed on the basis of core description and the study of thin section analysis, cathodeluminescence, SEM and X-diffraction. There were two types of reservoir in the basin and they were sandstone and carbonate reservoirs. After experiencing mechanical compaction + early cement (most primary pores were lost)→dissolution (secondary pores or enlarged residual primary intergranular pores were formed)→late recementing (partial secondary pores and residual primary intergranular pores were lost) →ferritization of iron\|bearing mineral (pores and residual primary intergranular pores were further lost) →diagenesis of residual primary intergranular pores, intercrystal pores, dissolution pores, micropore and microcrack (present pore) and pore evolvement, the sandstone reservoir was under the phase of early diagenesis B and late diagenesis A and B. The pore type was complex and dominated by secondary dissolution pores. The reservoir property was generally bad, but some good reservoirs still existed. The carbonate mud was under the phase of shallow\|middle burial and deep burial, and had generally a little amount of pores, bad property, and limestone caves developed in individual intervals after it suffered two types of diagenetic evolution: (1) The mechanical compaction and cementation formed micrite\|crystal bioclastic limestone, and local dolomitized by dissolution, cement and recrystallization; (2) The mechanical compaction and cementation formed grainstone contained terrigenous clast, intraclast, bioclast and micrite-crystal, and local dolomitized.