To meet a series of special performance requirements for concrete of engineering use, such as workability, cracking resistant performance, mechanical performance and durability, a new optimization method of concrete mix proportion design was proposed based on objective weight assignment and grey relational analysis. The orthogonal test method was used to study the effects of water binder ratio, sand ratio, total amount of cementitious materials, amount of mineral admixtures and mass ratio of fly ash to slag on C50 concrete performance, including workability, cracking resistant performance, mechanical performance and durability. Based on objective weight of each performance determined by the technology of objective weight assignment, the optimum mix proportion of C50 high cracking resistant and high performance concrete was achieved. The comprehensive performance of concrete with the optimum mix proportion was verified by experiments. The results show that this method can successfully optimize mix proportion of C50 concrete to satisfy multi purpose performance requirements. For experiment condition in this research, the optimum mix proportion of C50 high cracking resistant and high performance concrete is 030 for water binder ratio, 35% for sand ratio, 420kg/m3 for the total amount of cementitious materials, 30% for mineral admixtures amount and 2∶1 for fly ash to slag mass ratio. The verification experiment confirmed that the optimized mix proportion of concrete meet the needs of the desired multi purpose performance.