A new self-adaptive method to determine the calibration value in the effective distance of micro-pulse lidar (MPL) is proposed. A profile of aerosol backscatter coefficient, which is retrieved from MPL signal with the boundary value determined using the new method, is compared with the one retrieved from another lidar signal with the boundary value assumed around the troposphere. The comparison shows that the two profiles seem to be consistent with each other well. A group of lidar signal, observed continuously 12 hours, is retrieved with this method, which can accurately indicate the weather conditions. The result shows that the method has a good stability.