Lidar ratio of cirrus cloud has been attracted much attention as it is one of the most important parameters to study the optical properties of cirrus cloud. A new method has been introduced to deriving the lidar ratio of discontinuous high-altitude thin cirrus cloud by using the data from Mie scattering lidar measurements. The lidar ratio of discontinuous thin cirrus has been obtained after comparing the backscatter signal of the atmosphere observed in the condition of with and without cirrus in the usual days. The reliability and the disadvantage are also discussed by comparing with other methods.