High purity silica bricks have stable physical properties, except for the RUL (0.2 MPa) exhibiting extreme two different levels of high-level RUL T_0.6 of 1 683-1 686 ℃ and low-level RUL T_0.6 of 1 174-1 184 ℃. The low RUL phenomenon was researched, the formation reasons and solutions were analyzed in this paper. The low-level RUL T_0.6 of 1 174-1 184 ℃ of the un-burnt high purity silica bricks is a pseudo RUL T0.6 phenomenon for the transformation of crystalline morphology. The real RUL T_0.6 of the specimen hot treated at 1 093 ℃ is >1 680 ℃.Therefore, the un-burnt high purity silica bricks shall be hot treated at about 1 100 ℃ firstly before testing RUL. For the heating up of the lining of glass tank arch, baking curves with long holding time at 1 100 ℃ shall be strictly obeyed to avoid the obvious shrinkage negatively influencing the lining stability.