In this paper, the extinction property and optical depth of charged Martian dust at infrared band 3 THz–300 THz are studied using the Mie scattering theory. It is found that the extinction coefficients of Martian atmospheric dust and the dust optical depth (DOD) of the Martian atmosphere can be amplified significantly as the dust particles are charged. This extinction amplification has a peak, called amplification resonance, which shifts toward the upper left of the r-q parameter plane with increasing frequency. Here, r denotes the particle radius and q denotes the particle’s total net charge. The amplification of the Martian DOD is more significant at high altitudes than at low altitudes because the particles at high altitudes are smaller. For example, at an altitude of 30–50 km, the dust optical depth at 30 THz can be increased by 60–200%. However, at 3 THz–10 THz, the DOD at the near surface altitude (0–10 km) can still be enhanced by ~80%. This implies that by treating the Martian dust as uncharged particles, the dust density constructed from the Martian DOD data might be overestimated. The estimation error of the dust density of the Martin atmosphere may be reduced by counting the enhancement of the DOD that is caused by charged dust.