By using cirrus measurements with a Micro Pulse Lidar (MPL-4B) at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) from April to November in 2007, the statistical analysis is made for both cirrus height and thickness. The optical depth of cirrus is derived through transmittance method, and the relationship of the cirrus optical depth depending on the cirrus thickness and cloud base height is got. The results show that the mean value of the cirrus height at the SACOL is 10.16±1.32 km above sea level. The cirrus thickness varies between 0.3 and 2.8 km, and the mean value is 1.10±0.49 km. The cirrus optical depth varies between 0.003 and 1.057, and the mean value is 0.17±0.16. Most cirrus observed at the SACOL is thin cirrus whose optical depth is less than 0.3. From June to August, the cirrus height is higher and the optical depth and thickness are less than those in other months. The results show that the cirrus optical depth and thickness follow a positive linear relation.