The settlement observation usually adopts precision geometric leveling method, to improve the accuracy, generally requiring the value of central cross-hair to be in the range of 0.5m to 2.8m. However, it may easily exceed the range in the regions that have big value of slope. After analyzing, the conclusion is as follow: when the value of slope is certain, we can adjust the height of instrument, sighting distance and distance of slope, so as to make the value of central cross-hair in the range of our requirement. Thus make a compromise of the measurement efficiency and accuracy of measurement. When the values of slope are in the range of 10 degree to 20 degree, the critical values of sighting distance and distance of slope vary greatly. In the process of actual field measurement, combining with the slope acquisition method, taking the critical values of sighting distance and distance of slope as experience values, and it achieves a good effect.