The conglomerate in the Fourth Member of Xujiahe Formation, Upper Triassic, is widely developed in the front of the Micang—Daba Mountains. Based on the outcrops and wells analysis of these conglomerates, it is showed that the conglomerate of the 4th Member of Xujiahe Formation, Upper Triassic, is an alluvial fan—fluvial sedimentary gravels, whose thickness is between 0 to 70m and decrease from northeast to southwest. The gravels is generally poor sorted，sub rounded to rounded. We made a microcosmic analysis of conglomerate composition in the front of the Micang—Daba Mountains by polarizing microscope，it is found that the conglomerate consists of siliceous gravels, carbonate gravels, sedimentary quartzite gravels, siltstone gravels and volcanic gravels.However,the chert gravels is the main composition. We study individually volcanic gravels in detail, the results suggest that the Ordovician to Silurian volcanic rocks in Southern Qinling Mountains should be its source rocks. Combined with the discussion on source rocks of chert gravels, siltstone gravels and other gravels, it is believed that the conglomerate’s source rocks in the front of the Micang—Daba Mountains is the Sinian to Silurian strata in Southern Qinling Mountains. It is proposed that the source rocks which have been presumed have potential significances for understanding evolution of Sichuan Basin, sedimentary environment in the Late Triassic, and favorable reservoir distribution of the Xujiahe Formation.