Abstract: Composite materials with negative permittivity is widely concemed, and its basic structure is periodic etched continuous or discontinuous thin wires in the PCB. Due to the unique periodic structure, the effective permittivity of composite materials in some frequency band is a negative number. Similarly, as a result of the periodic structure, there possibly be some questions in the engineering applications, mainly the defect effect caused by the technical issues and the edge question caused by the period ended produce to the electromagnetism characteristic of composite materials to have the influence. Therefore, FDTD is used to numerically simulation analyze these two questions, The numeral simulation provides the theory basis for the engineering application of composite materials with negative permittivity.