In order to explore the engineering application performance of C70 high-strength concrete mixed with secondary fly ash and silica fume with low activity and high water demand ratio, the mixing ratio of silica fume and fly ash with different dosages is designed with C70 high-strength concrete of C3 project in Garden City as the research object, while an orthogonal comparison test is carried out. At the same time, the experimental design of C70 high-strength concrete is optimized according to the benchmark ratio test, and the results show that: 1) when the secondary fly ash content is 95kg/m³ , the engineering performance of C70 high-strength concrete is the best under the benchmark mixing ratio condition, and the concrete slump can reach up to 210mm ; Compared with the conventional benchmark mixing ratio, the strength increase in the early stage is increased by 69.6% , the increase in the medium strength is increased by 91.5% , and the peak intensity is reached by 109.3MPa ; 2) On this basis, by optimizing the silica fume content, using liquid silica fume with a concentration of 35% and a content of 50kg/m³ , the risk of shrinkage and cracking of concrete in the later stage can be effectively reduced, and the peak strength in the medium term can reach 110.2MPa , which is 8.23% higher than that when the solid silica fume content is 35kg/m³ , and the economic index is reduced by 3.2% per cubic meter, showing significant economic benefits. The results can provide a certain reference value for the engineering application of highstrength concrete, while help to improve the economic benefits of engineering projects, which has important promotion and guiding significance.