It is important to ensure construction safety to monitor settlement of foundation pit and the round buildings. The fixed height datum are usually selected in settlement observation, the stable basic benchmark is needed consequently, the stability of the operating control point play an important part in connection survey and settlement calculation. The analysis method of basic benchmark and operating control point are researched. Based on the settlement observation in foundation pit construction, the stability of basic benchmark and operating control point are analyzed by the survey data of datum network and the connection survey data of basic benchmark and operating control point, the accuracy of settlement data of foundation pit and the round building are ensured.