Composite plates are finding increasing application in aerospace, naval, and automobile industries and other high-tech designs because of their high specific stiffness and strength. However, during its vibration the composite plate can undergo cracks. Thus the natural frequencies of the plate will be influenced by these cracks. In this paper, a new element of hp FEM using the Mindlin plate theory from tree-node plate elements has been proposed for solving the free vibration of cracked orthotropic plates. This element performs well for elastic analysis and has the advantage that the crack can be easily incorporated in any location of the plate. The objective of the present work is to use this model on the triangular orthotropic plate, to investigate the variation of natural frequencies according to the dimension and location of the crack.