Based on the characteristics of pearlescent sand with many pores, low bulk density and low thermal conductivity, the influence of additive amount of pearlescent sand on the performance of bauxite castable was studied to improve the thermal insulation performance of permanent lining castable for tundish. The results show that with the increase of additive amount of pearlescent sand, the bulk density of castable decreases and the apparent porosity increases, which are related to the characteristics of pearlescent sand. Meanwhile, with the increase of the additive amount of pearlescent sand, water added of castable increases, and the in-situ pores formed by water evaporating inside castable increases during firing. Due to the decrease of the strength of pearlescent sand after water absorption and the limited bonding between pearlescent sand and the matrix in the castable, the flexural strength and cold compressive strength of castable decrease with the increase of the additive amount of pearlescent sand. Comprehensive analysis show that the optimum additive amount of pearlescent sand is 3% (mass fraction). The thermal conductivity of 3% pearlescent sand bauxite castable at high temperature of 400~800 ℃ is about 30%, smaller than that of conventional bauxite castable, which proves that the addition of pearlescent sand can significantly improve the thermal insulation performance of bauxite castable.