New zircon U-Pb age are obtained for late Early and Middle Triassic tuff layer from the Ganheqiao section, Wangmo country, Guizhou province. The first appearance of conodont Chiosella timorensis was discovered just 0.5m below the tuff, which is used to define the Olenekian-Anisian boundary in the lower/middle Triassic. Twenty zircons defined a weighted mean 206Pb/238U age of 247.6± 1.4 Ma (2σ). The new dates are in better agreement with a 247.2Ma age obtained from the Guandao section of Guizhou province, which were identified using TIMS method and were proposed for the boundary age of Olenekian-Anisian. The tuff layer found in the Ganheqiao section is wide distributed in southwest China. Our result defines a new dating for the regional stratigraphic correlation, and also provides a reliable dating for the duration of biological recovery in the early Triassic after the extinction of Permo-Triassic.