The mechanical characteristics of the large cylindrical structure with unloading plates are complex in practical engineering，and thus it is difficult to calculate by codes. Therefore，we build a model for this structure by finite element software to study its vertical tension，circumferential tension，vertical bending moment，circumferential bending moment，and the load distribution positions under the action of the quay crane load，wave force，and loading earth pressure. The results show that the load of a quay crane has little influence on the stress distribution of the whole structure of a large cylinder but has a significant impact on the bending moment at the top of the cylinder. The top of the cylinder is greatly affected by the vertical bending moment，while the lower cylinder is greatly influenced by the circumferential bending moment. Under the three kinds of loads，the maximum vertical and circumferential bending moments occur at the joint between cylinders，and the lower cylinder is under tension on the wave side and compression on the soil side.