In this paper, the damage degradation law and service life of mechanism sand concrete (MSC) were studied by composite salt freeze-thaw cycle test of tuff mechanism sand concrete (TMSC) and granite mechanism sand concrete (GMSC). The macroscopic indexes such as mass loss rate, relative dynamic elastic modulus, compressive strength loss rate and the microscopic indexes such as XRD and SEM were used to characterize the damage degradation law and corrosion mechanism of MSC. At the same time, the failure times of MSC composite salt freeze-thaw cycle were predicted according to the GM (1,1) prediction model. The results show that with the increase of the times of composite salt freeze-thaw cycle, the mass loss of the two kinds of MSC decreases first and then increases. The relative dynamic elastic modulus decreases gradually, and the compressive strength loss rate increases gradually. After 200 composite salt freeze-thaw cycle times, the mass loss rate of TMSC and GMSC is 1.29% and 1.75%, the relative dynamic elastic modulus is 63.30% and 58.70%, and the compressive strength loss rate is 42.16% and 45.58%, respectively. TMSC and GMSC fail after 204 and 193 composite salt freeze-thaw cycle times, respectively. The service life is 22.47 and 21.26 years, respectively. TMSC show better service life than GMSC under composite salt freeze-thaw environment.