The effects of pressure during ICP dry etching on electrical parameters of long wavelength MCT photo-conductive detectors were studied. It is found that increased etching pressure can deteriorate the electric performance, in which the carrier concentration of MCT devices is increased, carrier mobility is decreased and the resistance is increased. It can be explained as more Hg interstitial is induced under higher pressure, carriers experience an enhanced ionization scattering, and also more defects appear due to the enhanced lattice scattering. It is proved that the deterioration of MCT detectors’ performance is caused by higher pressure parameters during ICP etching.