Abstract: Abstract: As civil engineering develops toward high rise, large span, heavy load and lightweight structure, higher requirements in strength and performance of concrete has been put forward. Mineral admixture as the fifth component of concrete is gaining popularity in practical application and helps to improve the strength and durability of concrete. At present, researches are mainly focus on the kind of mineral admixture and its influence on concrete performance. Application of an amount of admixture is an important developing direction of high strength concrete. We prepared 2 kinds of high strength concrete containing 40% and 50% fly ash and slag respectively to identify the best quality proportion of mineral admixture in high strength concrete C50. Microstructures in different ages and phase in early age were observed with scanning electron microscopy and X-ray diffraction respectively so as to evaluate the influence of high quality proportion of admixture on high strength concrete from a microscopic perspective. Durability was assessed through chloride-ion penetration resistant test and rapid freezing-thawing test. And the comprehensive capability to resist frost and chloride ion permeation was reflected by the ratio of frost-resistant durability coefficient to electric flux value. The results showed that mineral admixture reduced the early hydration of cement. Peak value of calcium hydroxide was lower in the concrete with mineral admixture than that in the reference concrete, which led to the decrease in early strength of the concrete. Due to the super-composite effect of fly ash and slag, the later strength increased more rapidly and the structure became more compact, with some samples reaching or exceeding the reference concrete strength after 28 d curing. The strength would continue to improve in the long run. With the decline of the ratio of fly ash to slag, the strength of concrete after 28 d curing with 40% admixture decreased, while that of concrete with 50% admixture increased. Capability to resist chloride ion permeation improved as the increase of fly ash and the decrease of slag in concrete with a fixed share of total mineral admixture. The fixed share of fly ash and the increase of slag led to the decrease in that capability, suggesting fly ash had a better performance than slag in this respect. But the increase of total mineral admixture would undermine the capability of concrete to resist chloride ion permeation. Mineral admixture could better improve the frost-resistant performance of high strength concrete C50. With the decrease of the ratio of fly ash to slag, there were a greater mass loss, a greater decrease of relative dynamic elastic modulus and a greater decline of frost resistance after freeze-thawing. Concrete with higher percentage of mineral admixture had a slower decrease of relative dynamic elastic modulus, with a high value even after freeze-thawing of 300 times. The mixing quality of fly ash and slag was not consistent with the effect tendency of the frost resistance index and chloride ion permeability. But we found that the higher the ratio of frost-resistant durability coefficient to electric flux value, the better the comprehensive performance of frost resistance and chloride ion permeation resistance. Ratio of frost-resistant durability coefficient to electric flux value decreased in an approximately linear way with the increase of the ratio of fly ash to slag. D-value which was the ratio of frost-resistant durability coefficient to electric flux value could effectively evaluate the durability of high strength concrete C50 with high ratio admixture, and we proposed the proper mixing proportion was 50% for admixture amount and the content ratio of fly ash to slag was 4:1.