In this paper, the stability of the alternating direction implicit finite-difference time-domain (ADI-FDTD) method with split-field perfect matched layer (PML) is studied. From the theoretical stability analysis, it is found that the ADI-FDTD method with split-field PML will be unstable in the PML surface and inside the PML regions. The modified PML conductivity profiles are proposed to prevent the instabilities inside the PML regions. The effect of the PML conductivity profile on the stability of this scheme and the numerical performance of the PML are investigated. The theoretical results are validated by means of actual numerical simulation.