We study the generation of terahertz radiation from atoms and molecules driven by an ultrashort fundamental laser and its second harmonic field [1-8] by solving time-dependent Schr(o)dinger equation (TDSE).The comparisons of terahertz yields between one-, two-, and three-dimensional TDSE numerical simulations and electronic wave-packet dynamics show the wave-packets initial ionized states and subsequent acceleration in the laser field and rescattering with long-range Coulomb potential play key roles.We also present the dependences of the optimized phase delay and yield of terahertz radiation on the laser intensity, wavelength,duration, and the ratio of two-color laser components.The molecular alignment-dependent terahertz radiation yields are consistent with experiments [9] and their optimized two-color phase delays are less dependent on molecular alignment.