Early to Middle Triassic volcanic rocks are mainly distributed in the southwestern margin of Youjian Basin. There is no accurately ages and geochemistry study of those rocks. Now we choose a layered volcanic rocks between Luolou Formation(Lower Triassic) and Baifeng Formation (Middle Triassic) in Nalong,Guangxi area as our subjects. We analyzed zircon LA ICP MS U Pb isoplote age, major elements, trace elements of volcanic rocks in order to limiting the volcaniac rocks erupting time and discussing the source and tectonic significance. Volcanic rocks of Nalong yielded a LA ICP MS U Pb zircon isoplote age of 2412±19(MSWD=069)Ma which suggesting that these volcanic rocks erupted in the Middle Triassic. Geochemically of zircons is enriched in REE and have higher enrichment heavy REE. It has a strong negative Eu anomalies and positive Ce anomalies, with low Th, Th/U, Ce/Sm and δEu values and relatively higher Hf, Yb/Gd and U/Ce values which could indicate that zircon is a description of the continental crust in a deep melt sources where have been a stable plagioclase crystallization differentiation. The Whole volcanic rocks SiO2 are 5128%~5617% and have a lower TiO2(079%~128%) and higher Al2O3(1352%~1551%). These volcanic rocks have enrichment LILE and LREE and lack of HFSE, significantly similar to typical subduction related arc volcanic rocks. Ce/Pb and Nb/U values is similar to continental crust; Zr/Y and Zr values are higher which indicates that their mantle source is made up of Crust melt, Oceanic crust melt and so on. There have been added in deep sea sediments or crustal material during plate subduction. but the Ba/Th values (292~6975) is less than 300, indicating that mantle contamination is smaller. The determined of Island arc volcanic rocks in Nalong, Guangxi area indicate that there has being a subbuction zone of eastern part of Paleo Tethys Ocean during Late-Palezoic to Mesozoic.