Under the one-dimensional tight-binding miniband and contact interaction approximation, the extended semiconductor Bloch equation is employed to investigate the optical absorption spectra and evolution of the polarization wavepacket in semiconductor superlattices driven by a terahertz field, after the excitation by a femtosecond laser pulse. Under a direct current (DC) bias, the optical absorption spectrum changes from the absorption band in the case of zero field into a series of equal-distant peaks, so-called Wannier-Stark ladder, with the energy distance being proportional to the field strength. The Wannier-Stark ladder is the counterpart (in the frequency domain) of the periodic oscillation of electrons and holes in real space and in momentum space, i.e. Bloch oscillation. Under a THz alternating current (AC) field, the absorption spectrum also consists of a series of peaks, called dynamical Stark ladder, however, the energy distance is equal to the photon energy of the applied THz field and is independent on the field strength. Furthermore, the absorption edge is shifted. When a DC field and a THz field present simultaneously, the absorption edge does not shift, and the spectrum becomes richer. But the complicated features can be interpreted and identified by the combination of the Wannier-Stark ladder and the dynamical Stark ladder. The ratio of the Bloch frequency to the frequency of THz field and the ratio of field strength of the THz field to the frequency of THz field are two determinant quantities. If the ratio of the Bloch frequency to the frequency of THz field is an integer n, then n-order harmonic wave of THz photon is generated in one Bloch frequency. If the ratio of the Bloch frequency to the frequency of THz field is a fraction, then dynamical fractional Stark ladder is formed. On the contrary to this, the ratio of field strength of the THz field to the frequency of THz field determines the spatial extension of the polarization wavepacket.