The UNSAT unsaturated soil triaxial instrument was used to conduct cyclic loading and unloading tests under 50 kPa confining pressure in order to analyze the damage and deformation characteristics of polypropylene fiber-reinforced foamed lightweight soil. The mechanical properties and deformation laws of polypropylene fiber reinforced foam lightweight soil under different fiber mass fraction conditions were analyzed by using Poisson’s ratio, elastic modulus increase rate and elastic-plastic deformation trend as parameters. The research results showed that the initial elastic modulus increase rate was 56.88%-69.43% when the fiber mass fraction reached 0.50% to 1.00%. The fiber has the best effect on improving the initial defects of the foamed lightweight soil. The elastic modulus increase rate of the fiber-reinforced foamed lightweight soil sample firstly increases and then decreases with the increase of the number of cycles. The Poisson’s ratio increases with the increase of the number of cycles, and tends stable after the first 2 and 3 cycles of loading until the sample is broken. The ratio of the axial elastic strain to the total strain of the fiber-reinforced foam lightweight soil gradually decreases as the number of cycles increases, and the internal damage and deformation of the sample gradually accumulate.