The modification mechanism of polymer cement concrete (PCC) was analyzed by differential thermal analysis, SEM electron microscopy and pore structure tests, and verified by combining indoor macro road performance test and test road drilling test. The results show that with the increase of polymer content, the amount of Ca(OH)2 in cement hydrate decreases, the pore structure is improved, the polymer film tends to be continuous and complete and intertwined with cement hydrate to form a network structure, the internal defects of concrete are reduced, and gradually transformed into a continuous dense structure, accompanied by a large increase in flexibility. The indoor macroscopic test and on-site test also confirmed the following modification mechanism: due to the incorporation of polymer to improve the microstructure of cement concrete, the pavement performance of concrete was significantly improved, and the composite pavement performance was excellent.