The experimental equation of state and temperature data of the dense gaseous H2 + D2 mixtures under multi-shock compression were presented in a pressure range of 2–36 GPa and a temperature range of 2300–5300 K. The strong shock wave was produced using the flyer plate impact by accelerated up to 5.1–6.2 km/s with a two-stage light-gas gun and introduced into the plenum gas sample, which was pre-compressed from environmental pressure to 30–40 MPa. Time-resolved spectral radiation histories were acquired with two sets of multi-wavelength channel pyrometers, which were used to determine the shock velocity and shock temperature in the sample. Shock pressure and particle velocity were obtained by the impedance matching method. The experimental data prove the validity of self-consistent fluid variational theory (SFVT) model in the partial dissociation region. The time-resolved spectral radiation histories along with the SFVT calculation show that the shocked gas samples lose their transparency in visible light wavelength ranges of 400–800 nm at about 12.99 GPa and 4413 K or higher.