Abstract: Finite-Difference Time-Domain (FDTD) method is a simple and effective solution to calculating the dispersionand radiation of the electromagnetic wave in time domain, it is widely used in solving the problems of electromagnetic field, butit only can be used in the limited areas because of the limited capacity of computer, so it is necessary to set the absorbingboundary conditions to simulate open electromagnetic problems, and perfectly matched layer (PML) is a good choice. In thispaper, an algorithm of implementing the PML is presented for truncating FDTD computational domains. Compared with the conventional method, this algorithm is based on incorporating the Z-transform method into the FDTD implementation. Theadvantage of this method is its simplicity. In addition, the iterative equations are independent of the fictitious material propertiesof the FDTD computational domains. Numerical examples demonstrate the validation of this algorithm.