Abstract: In practical tilt tidal observation, it is genera case that a large phase difference and sensible anomaly of the North-South commponent and considerable discrepancy between observations carried out with different instruments at the same station be experienced. These evidently cannot be explained by thermal or oceanic indirect effects. In this paper, after theoretical study of every probable cause, a conclusion has been drawn as follows. Because most tidal tilt stations are located in the middle latitudes, the error of azimuth of the pendulum beam, cavity effect and the smaller amplitude of the North-South component might be the main soures leading to the above anomalies.