Target slice thickness in a Spallation Neutron Source (SNS) solid target system has great influence on the target normal operation. In this paper, a new optimization method is proposed for the target cooling system to analytically optimize the target slice thickness. We theoretically analyze the factors influencing the surface temperatures of target slices, simplify the heat source distribution to obtain the relation between the surface temperature and the thickness of a target slice, and finally get the optimal slice thickness through uniformizing the surface temperatures of the slices. For verifying the feasibility and reliability of the target cooling system with the optimized target slices, two 3-dimension physical models of the original and the optimized target systems are created for numerical simulation. The comparisons show that the maximum temperature of the cooling water after optimization is below the limitation, and the maximum temperatures of every tungsten target slice are almost uniform and lower than 180.0 degrees C. That is, the cooling water effectively remove the heat generated by spallation reaction, and the volume flow rates of the cooling water in every slits are uniform, which indicates that the optimized structure satisfies the demand of the target system normal running and improves the performance of the cooling system. Therefore, the proposed method is convenient and efficient for the optimization design of target slice thickness. (C) 2013 Elsevier Ltd. All rights reserved.