In order to certificate the electromagnetic characteristic of left-handed materias (LHM), we adopt unsplit finite-difference time domain method (FDTD) to the ideal Drude model of LHM. This method does not need to split the electric and magnetic fields and does not need the use of special treatment of PML. PML and working space can be converted with the parameters. The penetrating wave will be attenuated in the PML which is set up by lossy dielectric. So it is an effective method to analyze dispersion and anisotropic material. Thus we can confirm the LHM and its unique characteristics such as negative refraction, convergent and phase compensation and verify the effectiveness of analyzing LHM using unsplit FDTD.