Abstract: In order to study the size effect law of carbon fiber reinforced polymer (CFRP) constrained coal cylinders, a numerical model of coal circular confined by carbon fiber reinforced polymer (CFRP) sheet is established by a three-dimensional PFC-FLAC coupling method. The validity of the model was verified with experimental data. On this basis, the study of the size effect of 0, 1, 2 and 3 layers of CFRP sheet on different sizes (50 mm, 100 mm, 150 mm) of coal cylinders were studied; the functional relationship of the evolution law of compressive strength under different layer number (L) is obtained; the functional relationship of elastic modulus evolution under different number of layers is obtained; a modified Richart strength analysis model of coal cylinder confined by CFRP sheet is established. The results show that when the number of CFRP sheets is constant, the compressive strength of coal cylinders is constrained by different sizes of CFRP sheets, and the size effect is obvious; the relative peak strength enhancement ratio of coal cylinder constrained by CFRP sheet increases with the increase of the size. The elastic modulus of a coal cylinder with a diameter of 50 mm increases with the number of CFRP layers. The elastic modulus of a coal cylinder with a diameter of 100 mm and 150 mm increases first and then decreases at 0≤L≤3 layers, showing an obvious layer effect law. The accumulation of cracks increases with the increase of the number of CFRP layers.