The modified rubber concrete’s mechanical properties were evaluated after adding metakaolin to NaOH pretreated rubber concrete. The impacts of metakaolin on pore structure characteristics and hydration product content of the material were analyzed using scanning electron microscopy（SEM）， mercury porosimeter（MIP） and thermal gravimetric analyzer（TG-DTG）. The results show that incorporating metakaolin in modified rubber concrete can enhance the quantity of hydration products， improve the interfacie transition zone quality amidst the aggregate and cementitious material， refine the pore structure， and reduce internal porosity， resulting in improved mechanical properties. The mechanical properties of the modified rubber concrete exhibit an initial increase and then a decrease with rising metakaolin content， with the most significant improvement observed at a content of 15%.