Vitrification enables to create complex structure with a large degree of disorder, which provides a new solution to improve the performance of lead telluride (PbTe)-based thermoelectric materials by reducing the lattice thermal conductivity. Yet, it is an extreme challenge to vitrify PbTe-based alloys due to the incomplete knowledge of the glass formation mechanism. Here, the glass formation of PbTe-based alloys is studied by jointly concerning thermodynamics and kinetics. The comparison of (PbTe)x(Ga2Te3)100-x and (PbTe)x(In2Te3)100-x alloys showed that low entropy of fusion(∆Sm) and deep eutectic fashion are the two keys in glass forming ability(GFA). Novel (PbTe)x(Ga2Te3)100-x glasses are prepared and the glass-forming region is identified to be the composition range of x = 52 ~ 64. An extremely low thermal conductivity of the best glass component (PbTe)61(Ga2Te3)39 is determined with the value of ~ 0.1 Wm−1K−1 at 300 K.