The steel-concrete immersed tube prefabrication yard of Shenzhen-Zhongshan Bridge is upgraded from the Hong Kong-Zhuhai-Macao Bridge. The original caisson dock gate and entrance need to be widened and renovated. We propose three sets of overall plans including the large and small dock door，widening both sides of the old dock door，and building the new dock door，put forward three schemes including welding of rebar lap，planting bar joint，and pre-stressing joint for the plans of widening both sides of the old dock door，carry out the numerical analysis on the stress of the broadened dock door structure，and propose the schemes of steel-concrete structure and all concrete structure for the plan of building the new dock door. Based on the actual site condition and the analysis results，we compare and select the above schemes for the construction design. The results show that the three upgrading schemes of dock gates are feasible in construction technology. The widening dock gate scheme has great advantages in construction period and cost. The floating dock gate with full concrete structure is finally selected in the specific project implementation.