The design of sacrificial anode cathodic protection lacks optimization approaches for the dimensions of single anode and the overall scheme. The concepts of slenderness and flatness are firstly introduced to solve this problem. The relationship between the dimensions of the sacrificial anode without coating and the total quantity and the mass of the required sacrificial anode is deduced based on the specifications. The feasible region of the dimensions of the sacrificial anode is then determined according to the polarization requirement of the structure and the consumption requirement of the sacrificial anode material. Finally, an integrated optimization model is established with the economic index in order to give the solution. This optimal design method can determine the dimensions of the sacrificial anode and get the general scheme with the optimized economy.