A set of clastic rocks in the Biliutai area of Baarin Left Banner of Inner Mongolia, characterized by sand and slate assemblages, was considered as the Early Permian deposits previously. The 100 detrital zircons from the feldspar lithic sandstone of the strata were dated by LA ICP MS U Pb method. The result shows that the age of the detrital zircons can be mainly divided into four groups：253~298Ma，309~362Ma，428~595Ma，851~1526Ma, of which, the 253~298Ma age data show a peak age of 266Ma. The age of 266Ma limits the sedimentary period of the strata, which should be the Late Permain deposits. Moreover, the age characteristics of the detrital zircons and the lithologic associations of the strata can be compared with those of Linxi Formation in a regional scale, so the strata should be assigned to the Linxi Formation. The characteristic of the age spectra of the detrital zircons reflects that there were multiple provenances forming the strata, and the provenances were mainly from northeast blocks rather than North China plate, which indicates that North China plate had not yet collided with Siberia plate to close up completely in the Late Permian. And the 253~298Ma age coincided with that of the magmatic event which was related to plate subductions and collisions near Xar Moron River suture zone, and that indicates that the final closing time of the two plates was later than 266Ma.