Widely distributed in Southern Qilian, the Silurian Balonggonggaer Formation(B.F) differs greatly in its formation age and tectonic properties. To illustrate the age and geological significance of the dacite- rhyolite from the B.F in the Tuergendaban, representative rocks were selected for the main and trace elements, LA- ICP- MS zircon U- Pb Chronological analysis. Geochemical results indicate that volcanic rocks of the B.F are high potassium, calcium alkaline and peraluminous, and experienced certain cystallization differentiation during diagenesis. Enrichment in K, Pb and LREE, relatively depleted HFSE, such as Zr、Ce and Nb, with obvious P, Ti negative anomaly. The ratio of LREE / HREE is 6.98~10.13, δ Eu between 0.40~0.54 with negative anomaly, indicating that REE fractionation is obvious. The right- inclined distribution pattern of REE in each sample is basically similar, suggesting that they have similar magmatic sources and processes. The three accordant ages through LA- ICP- MS zircon U- Pb were 438.1±2.2Ma, 403.0±2.6Ma, and 404.9±2.8Ma, indicating that the geological period of the formation of volcanic rocks was Early Silurian- Early Devonian. The comprehensive comparison shows that the former Silurian B.F should be disintegrated and re- understood. The volcanic activity of the B.F in Tuergendaban area are close to the same period of the southern Chaidamushan granite magma activity, both may be related with the collision, which the Qilian block from the north to the south thrusted over the Qaidam block, form a series of continuous magmatic intrusion activities.