The timedomain radiation characteristics of the resistanceloaded dipole ante nna with dielectric block parallelly connected to one side of the feeding region are studied by using finite difference time_domain(FDTD) method and perfectly m atched layer(PML) technique. It is found that this kind of antenna has very well directive property. The influences of the size and dielectric constant of the l oaded dielectric block on the radiation characteristics of the antenna are analy zed. The optimum structure parameters of antennas with very well directivity and enough efficiency are given. The low profile property of this kind of antenna m akes it easier to integrate with circuit. It is preferable for the ultrawide b and wireless communication system, such as UWB system, to use this kind of anten na.