The glass mortar bar test (GMBT) is a method to evaluate the effectiveness of mineral admixtures (MA) on suppressing ASR expansion. GMBT uses 5% fused silica glass and 95% standard sand as the aggregate, Portland cement as the bonding compound， and substituting mineral admixtures with same quantity by volume of cement, and performs in accordance with ASTMC1260 94 accelerated mortar bar test (AMBT) to detect the ASR expansion. If the expansion of GMBT is less than 0.10%, the expansion due ASR can be suppressed effectively by using the MA. Because the activation of the aggregate is relatively stable, the results of GMBT have a good repeatability. The suitability of simulating natural aggregate by using fused silica glass was proved additionally by results of differential thermal analysis, scanning electronmicroscope and Xray diffraction.