Abstract: A monitoring method of bottom heave based on pressure difference sensing technique was proposed for the monitoring of foundation pit. Firstly, the principle of pressure difference sensing technique was analyzed. Secondly, the pressure difference sensing system and corresponding auxiliary system were introduced. Thirdly, the temperature stability of the monitoring system was verified by the model test. Finally, the monitoring system was applied to the engineering practice, and the monitoring results were analyzed. The results show that the bottom heave increases with increasing of the excavation depth. When the excavation depth is small, bottom heave starts with the beginning of excavation, and ends with the end of excavation. When the excavation depth is large, bottom heave starts with the beginning of excavation, but continued to increases at the end of excavation. When excavating the same thickness of soil layer, the deeper the soil, the greater the heave, and the longer the time of bottom soil stable.