Silver-Indium-Cadmium (Ag-In-Cd) is commonly used as the neutron absorption material in PWR, and its swelling under reactor irradiation condition may lead to outward deformation of control rod cladding, and finally affect RCCA dropping. In severe cases, rod dropping time exceeding its limit regulated in operation technical specification and even RCCA sticking caused by Ag-In-Cd excessive swelling may occur, which will threaten reactor safety shutdown. The influence of different swelling forms on the dropping time of RCCA is studied in this paper, and finally the absorber design is optimized based on current PWR absorber design. The results show that the swelling of control rods has little effect on T5, but mainly affects the dropping time T6 in the dashpot section. Different swelling positions have different effects on the dropping time, and the optimized design can improve this swelling effects.