Geopolymer recycled aggregate concrete（GRAC） was prepared by replacing cement with geopolymer and natural aggregate with demolished concrete. The effect of the modulus of water glass（n） on the mechanical properties of GRAC was studied and the mechanism of influence of its microstructure on the mechanical properties was analyzed. The results show that there are two kinds of gel structures in geopolymer hydration products， aluminium-modified calcium silicate hydrate（C-A-S-H） layered structure and sodium aluminosilicate hydrate（N-A-S-H） network structure， both of which contribute to the strength of GRAC. The compressive strength of GRAC increases with the decrease of n. The dimensional conversion factor of compressive strength of GRAC is correlated with n， and the standard deviation of compressive strength decreases with the increase of n. In the constitutive equation of compressive strength of GRAC with n as variable， the up-portion coefficient has polynomial relation to n， and the down-portion coefficient has rational fraction relation to n.