The fatigue behaviour of three types of fabric conveyor belt subjected to shear loading is studied. The fatigue phenomenon of belts is explained by the decrease of shear strength, which is determined as an ultimate angle initiating the lamination failure of the central rubber layers. Tests with precycling have shown that the permanent shear strength is diminished during precycling and can be modelled by power functions of the number of cycles, called fatigue strength functions (FSFs). Two main hypotheses of FSFs' existence and state equivalence are tested. A comparison between the proposed method and a linear damage accumulation rule is also carried out for two-level loading.