A theoretical model for the free vibration characteristics of Functionally Graded Carbon Nanotubes Reinforced Composites （FG-CNTRCs） thin cylindrical shells considering the scale effect of Carbon Nanotubes （CNTs） was established. First， the nonlocal Eshelby-Mori-Tanaka （EMT） constitutive model of macroscopic CNTRCs was developed based on the EMT method and nonlocal theory by considering the orientation and scale effect of CNTs. Then， based on the Kirchhoff-Love cylindrical shell assumption， the free vibration governing equations for FG-CNTRCs cylindrical shells on the visco-Pasternak foundation in the thermal environment ware derived by applying the Hamilton principle. The natural frequencies of the simply supported cylindrical shells at both ends were obtained by the Navier method， and the results were compared with those in the literature to verify the correctness of the model and method. Finally， the effects of nonlocal parameters， volume fraction and distribution of CNTs， length-to-thickness ratio of cylindrical shell， ambient temperature， and foundation parameters on the free vibration characteristics of simply-supported FG-CNTRCs cylindrical shell were analyzed. It is found that considering the scale effect of CNTs can reduce the bending stiffness of FG-CNTRCs cylindrical shells. The influence of ambient temperature on the imaginary part of the natural frequency of simply supported FG-X-CNTRCs cylindrical shell increases with the increase of CNTs volume fraction， and the influence of length-thickness ratio and foundation damping parameters on the imaginary part is coupled.