This paper studied the influence of temperature increase rates (5, 10 ℃/min), duration at target temperatures (1, 2 hours) and cooling methods (natural cooling, water cooling) on the residual compressive strength of alkali activated slag concretes after high temperature. The microstructural change of the alkali activated slag matrix with temperature elevation was also studied to analyze the strength change. The results show that when the higher temperature increase rate was used, within 400 ℃, the influence of thermal stress was not sufficient, and a shorter duration in heat could remain the strength of concretes at a considerable level; with temperature elevation to 800 ℃, residual strength decreased dramatically with the increase of thermal stress; afterwards, thermal stress has achieved a certain extent, and a shorter duration in heat remained the strength. Increase in duration at target temperature has intensified the deterioration of alkali activated slag matrix and matrix-aggregates ITZ, resulting in the decrease of the residual strength. Water cooling has lowered the temperature of C-S-H hydrates to decompose, as well as resulted in thermal stress in concretes, and consequently limited the remain of the residual strength.