In this study, the viscosity of unidirectional CFRTP laminates near the melting point was evaluated to discuss the relationship between the thermal fusion conditions and the flow of fiber and matrix. The laminates were regarded as a fluid flowing in a direction perpendicular to the fiber. The microscopic flow of the fiber and matrix near the melting point was observed during a parallel plate compression test. Based on this observation, viscosity and flow properties were evaluated by the finite element method. The results of the parallel plate compression test showed that the test conditions and the decrease in the thickness of the laminates are related to the apparent viscosity of the unidirectional plate. In addition, cracks in the direction of the maximum shear stress were detected via in situ observation near the melting point of the matrix. The occurrence of this phenomenon depended on the apparent viscosity of the unidirectional laminates and it was found that no cracks occurred when the apparent maximum viscosity of the unidirectional laminates was lower than a certain threshold.