This letter studies digital/analog hybrid precoding for wideband millimeter wave (mmWave) systems with multi-subarray architecture. By exploiting the mmWave propagation property that the dominate signal energy arrives at the receivers through some concentrated directions, we first present the single carrier transmission with time delay compensation technique performed at the base station, which can efficiently suppress inter-symbol interference. Then, in order to address the number of radio-frequency chains limitation, we propose a joint subarray selection and precoding design scheme by using the group sparse approach. Numerical results also demonstrate the effectiveness of the proposed scheme.