By the observation of the drilling core, it is found that a new type of reservoir, named gravel-sized grain carbonate rocks, is mainly distributed in the Feixianguan Formation of Puguang Gas Field in the foreslope of platform. Based on the analysis of gravel composition, development scale, grain size and degree of roundness, it could be divided into calcirudyte and dolorudite. It is shown that small scale calcirudyte is mainly formed by long distance transportation and with relationship to the turbidity current; and large scale dolorudite is mainly formed by no moving or by short distance transportation and with relationship to the collapsing sediment. In the sedimentary model of gravel-sized grain carbonates in slope belt in Feixianguan Formation of Puguang Gas Field, the source of calcirudyte is from the carbonate platform, and the big scale dolorudite is usually distributed in the upper slope belt where the favorable reservoir is well developed, but the thin calcirudyte is distributed in the lower slope where the reservoir is not developed.