Graded lattice structures (GLSs) have drawn much attention in engineering and biological areas due to the enhanced mechanical properties and energy absorption capacity that benefited from the graded porosity design. The aim of this study is to investigate the effect of gradient on fatigue behaviours of lattice structures. A GLS consisted of the Gyroid unit cell, one of the triply periodic minimal surface structures, was designed with continuously varied porosity from 60% to 90%. Uniaxial compressive testing and compression-compression fatigue testing were conducted on the Ti-6Al-4V Gyroid lattice structures with both uniform and graded porosity fabricated by selective laser melting. All three typical fracture modes and mixed fracture modes were all observed on the fracture surfaces of struts after fatigue testing. The fatigue life of Gyroid GLSs is 1.21~1.67 times that of uniform counterparts with an identical overall porosity. The enhancement mechanism on fatigue properties coming from gradient design is elaborated through finite element analysis and experimental characterization. The lower level of tensile stress, bigger macro-area and micro-plastic zone on the strut surface of the main loading-bearing constituent of Gyroid GLS relieve the stress concentration around the crack tip, thus, lower the crack propagation rate and provide stronger fatigue crack resistance. Furthermore, the struts in the main loading-bearing constituent are more prone to stretching, therefore, provide long-term carrying capacity even after the occurrence of penetrating cracks. Experiment results show that the carrying capacity can be still provided by these struts even with penetrating cracks.