Abstract: A method based on CACO (chaos ant colony optimization) algorithm and 2-D solidification and heat transfer model was presented to optimize the water distribution parameters in secondary cooling for continuous casting-a multi-criteria optimization problem. The solidification and heat transfer model introducing volume control method was mainly used to simulate the continuous casting process, so as to investigate the surface temperature distribution of strands and characters of parameters' search space, while the CACO algorithm was used to solve the optimization problem of water distribution parameters in secondary cooling. Characterized by the chaotic and self-organization behavior in ants' foraging process, the algorithm rises above such defects of conventional ant colony algorithm as slow convergence rate, easy to stagnate, and low ability in global search. CACO thus shows the superiority in both convergence and robustness when solving multi-criteria optimization problems. The proposed method in application for the optimization of secondary cooling parameters resulted in highly improved quality of CC billet.