Based on the urban shantytown renovation project in Hongguang Town, Helan County, Ningxia, in Northwest China, the influence of fly ash and silica fume admixture on the mechanical properties of Self-compacting Concrete (SCC) was tested and analyzed in this work. The experimental tests including compressive strength, splitting strength, triaxial strength and an ultrasonic nondestructive test. Furthermore, the Back Propagation (BP) neural network algorithms were established. The results show that there is an obvious difference between the development law of compressive strength of SCC and that of ordinary concrete. The splitting pressure ratio of SCC is 1/10 to 1/8, while that of ordinary concrete is 1/13 to 1/10. Moreover, the peak strain, peak stress and initial stiffness of SCC increase with the increase of the confining pressure when compressed from three directions. In addition, the ultrasonic amplitude of SCC can reflect the changing laws of its compressive strength. As a conclusion, the addition of fly ash and silica fume increases the splitting pressure ratio of SCC. More importantly, the compressive strength formula for SCC with silica fume and a low content of fly ash is proposed, and the model equation between the amplitude and compressive strength is given. This study provides a reference for the mixture ratio of fly ash and silica fume in the application of SCC.