Abstract: A research on seismic performance optimization of Y-shape eccentrically braced composite frame is conducted in this paper. A total of three typical structures of five-story, ten-story and fifteen-story are selected as the research objects, and the efficient fiber beam model considering the spatial composite effect of slabs is adopted to simulate the research objects. A genetic algorithm is developed for the Y-shape eccentrically braced frame, and the chromosome coding rules, fitness function, termination condition and the rules of selection, crossover and mutation are specified. This algorithm is then applied to the optimization of the distribution strategies and mechanical parameters of eccentric braces, respectively. The results indicate that the proposed genetic algorithm can rapidly find the optimum solution for the seismic performance optimization problem of Y-shape eccentrically braced composite frame, and shows good convergence. Compared with traditional traversal algorithm, the genetic algorithm can significantly reduce the calculation cost of optimizing the distribution of the eccentric braces when applied to mid-rise and high-rise structures. According to the parametric analysis on the cost of the genetic algorithm, the species population, elimination ratio and mutation ratio are slightly growing with the increase of story numbers. For the distribution optimization problem, the species population is suggested to be 4~12, the elimination ratio and mutation ratio are both suggested to be 10%~20%. For the mechanical parameter optimization problem, the species population is suggested to be 4~8, the elimination ratio is suggested to be 20%~30%, and the mutation ratio is suggested to be 10%~20%.