In examining dynamic problems of unidirectional fiber reinforced composites, especially high speed problems such as impact loading, and dynamic failure process, we must consider elastic waves which propagate in composites. Though some theoretical analyses have been made on these problems, the general aspects have not been fully clalified because of their heterogeneity and anisotropy. Furthermore, as composite materials have many types of inherent defects, numerical analyses are more effective in order to analyze such complicated dynamic properties of composites in detail. In considering the problem of elastic wave propagation, the correspondence between wave length and size of components which make up the composite is very important. For the relatively long wave problems, FEM structual analysis programs in which homogeneity and anisotropy of composites is assumed are effective to some extent. However, they are not practically applicable in cases where the wave length is about the same size as fibers, since the number of nodes increases tremndously, requiring a considerably high memory capacity and increasing the computation costs. In this paper, we propose a new two-dimensional wave propagation model of a unidirectional fiber reinforced composites. The results are summarized as follows : (1) Dynamic simulations are carried out based on this model by means of a finite difference scheme. These simulations are shown to be accurate enough by comparing with the analytical solution by the elastic wave theory and FEM solitions. (2) Longitudinal waves and transverse waves propagating parallel to fibers are examined by the simulation, which shows that the material is more effectively characterized by the shape of elastic wave if a pulse wave is used in ultrasonic detection. (3) The reflection and mode transition of elastic wave at the boundary can be observed in detail by the present simulation model. (4) Fiber defects of unidirectional fiber reinforced composite are successfully evaluated by the elastic wave propagation.