To further understand the working mechanism of the gravity quay unloading slab，a finite element generalized model was established，and the numerical calculation and analysis of the gravity quay with unloading slab was performed. The results show that：1）The overall structure is a deformation mode rotating around the unloading plate and behind the wall. 2）The upper wall is displaced behind the wall and squeezes the back soil to form a passive pressure zone，and the increase rate of soil pressure at the back of the wall is 40.2%. The displacement of the lower wall toward the front of the wall forms an active unloading zone，the unloading efficiency of the earth pressure on the back of the wall is 35.4%，which cancels each other out，the change of the lateral earth pressure on the back of the wall has a limited effect on the structural stability. 3）The active earth pressure formula is multiplied by an increase factor of 1.5，and the earth pressure on the lower wall can be directly calculated according to the Rankine active earth pressure formula. 4）The lateral earth pressure on the upper wall increases，the lateral earth pressure on the lower wall decreases，and the unloading plate the increase in the weight of the top filler （including ground load） and the increase in the weight of the cantilever section contribute to the anti-sliding stability of the terminal are -21.1%，24.6%，75.6%，and 20.9%；the contribution to the anti-tilt stability of the terminal are -13.4%，6.6%，86.3% and 20.5%，the latter two are the main contributing factors. 5）The stability of the dock increases with the cantilever length of the unloading plate，and the optimal position of the unloading plate is about 0.6 times the wall height.