Experiments have been conducted with Huolinhe lignite low temperature ashes (HLH-LTA) to investigate the mineral behaviors under gasification atmosphere (H2/CO2=1:1, volume ratio) with the temperature increase by SEM and XRD. The results show that the contents of SO3 and alkali metal oxide (e.g. K2O, Na2O) are higher in the HLH-LTA than that in laboratory HLH ashes. The formation of some low-melting ferrous eutectic compounds causes the initial melting temperature of HLH-LTA is lower about 300 °C than its deformation temperature. The formation of slag during HLH fluidized-bed gasification is the results of the interaction among minerals and phase changes with the temperature increases under reducing atmosphere.