A set of Middle Devonian Dushan reef-shoal facies dolostone reservoir that is more than 600m thick and full of karst pores and caves is drilled in Well AS-1 in Qiannan Depression, Guizhou province. It is shown that the development of the Dushan reservoir is controlled by high-energy sedimentary environment, sea-level changes and late deep-buried hydrothermalism. Abundant dissolved pores and caves formed in the reservoir because of keeping subjection in frequent geological processes involving penecontemporaneous sea level eustasies, local exposures, fresh water leaching and late deep-buried hydrothermal dolomitization. The evidences that the dolostone forms from deepburied hydrothermal dolomitization are the hydrothermal products, such as saddle dolomite, zebra texture and secondary granular pyrite, and the fact that the values of oxygen isotope obviously deviate from the background value. This unique mechanism of Dushan dolostone is significant to predict where the development zones of the reef-shoal facies reservoir are.