In order to investigate the accuracy of the in-situ test results of uplift piles under the foundation pit, the model test method was used to study the stress response and deformation law of uplift piles under excavation unloading conditions by changing the excavation range and pile length of the foundation pit, and then reveal the bearing mechanism of uplift piles. The results show that when the size of the foundation pit is fixed, the normal stress of the uplift pile at the same depth is the same; Under the condition of the same pile length, the ultimate bearing capacity and pile top displacement of uplift piles are not the same under different foundation pit sizes; When the width of the foundation pit is greater than the critical value of "boundary effect", the increase of the width of the foundation pit has little effect on the bearing characteristics of the uplift pile; When the size of foundation pit is fixed, the bearing capacity of uplift pile can be significantly increased by increasing the pile length.