Abstract: Using expanded perlite (EP) as the internal curing material, the concrete compressive strength test and EP-concrete interface SEM test were carried out, and the influence of the volume admixture rate, prewetting rate and particle size of EP on the growth of concrete compressive strength was studied. Finally, the expression of the volume fraction of the internal curing paste and the degree of hydration reaction under the influence of the three factors of EP volume admixture rate, prewetting rate and particle size was obtained through formula derivation. And combing with Powers model and the model about concrete compression strength with porosity, a mathematical model of EP internal curing concrete compressive strength was established. The results of the compressive strength test show that the internal curing effect of EP can increase the compressive strength of concrete and its growth rate. The 90 days strength of concrete with EP volume admixture rate of 30% exceeds 13% of normal concrete (NC) at the same age. The 90 days strength of concrete with EP prewetting rate of 30% and 50% exceeds respectively 6.3% and 5.3% of NC at the same age, and the strength growth rate shows a trend of first decline and then rise. The 90 days strength of the concrete with EP particle sizes of 0.2-0.5 mm exceeds 6.4% of the NC at the same age, the strength increases slowly in the early stage and rapidly in the later stage. The 90 days compressive strength of the concrete with EP particle sizes of 1.5-3.5 mm and 0.5-1.5 mm increases rapidly in the early stage, and then gradually decreases and stabilizes in the later stage. The SEM test results show that the internal curing effect of EP can promote the cement hydration continuing. The products of hydrated calcium silicate (C-S-H) and ettringite (AFt) increase in quantity, and their arrangement gets denser, which can fill the micro-cracks of the EP-concrete interface. The pores of EP provide growth space for hydration products. The mathematical model verification results show that the mathematical model curve of the compressive strength of concrete internally cured by EP is in good agreement with the 90 days strength test value, and the error between the theoretical value and the test value is less than 12%.