Abstract: To explore the influence of pore structure of nano-SiO₂ fly ash concrete on compressive strength, the content of nano-SiO₂ additional rate 1%, 3%, 5% and 7%, and fly ash additional rate 10%, 20% and 30%, respectively, the water to binder ratio 0.35, and the two were mixed together for the test. Determine the cube microstructure compressive strength 3, 7 and 28 day. The pore structure and micro morphology were comprehensively analyzed and studied by nuclear magnetic resonance technology, field emission scanning electron microscope and differential thermal gravimetric technology. The primary and secondary factors affecting the compressive strength of concrete are found out by gray correlation entropy analysis, and the GM（1, 4） gray prediction model was established. The results show that the nano-SiO₂ and fly ash can promote the hydration of concrete, and improve the early compressive strength of concrete, meanwhile the optimal mix proportion is 20% of fly ash and 3% of nano-SiO₂. The main factors affecting the compressive strength are(0,0.01μm pore size ratio,(0.01,0.10μm pore size ratio and bound fluid saturation, which are used to establish a GM（1, 4） gray model. The average relative errors between the predicted values of 3, 7 and 28 day and the experimental values are 3.58%, 4.37% and 2.88%, respectively. Using the pore structure to predict the compressive strength of concrete has better accuracy. This study can provide reference for the application of nano-SiO₂ and fly ash in concrete engineering.