Alkali aggregate reaction is one of the common hazards in civil engineering. In order to promote the application of geopolymers，the alkali aggregate reaction and deformation behavior of alkali-activated metakaolin base polymer mortar mixed with basalt aggregate should be analyzed under high temperature and high alkali environment. Metakaolin based polymer mortar mixed with two different particle sizes of basalt aggregate was prepared. The deformation behavior was studied，when those was put in 80℃，2 mol/L NaOH solution curing for 14 days. The composition and microstructure of raw materials and products were analyzed using XRF，XRD，SEM. The results show that alkali silicon reaction of basalt is induced in geopolymer. However，the alkali silicon reaction is not sustainable. The slurry part of geopolymer will form zeolite structure eventually. A large number of harmful alkali can be absorbed and solid dissolved resulting from the special cage structure. Consequently，geopolymer material can effectively avoid the harm of alkali aggregate reaction.