Abstract: Biological soil crusts (BSCs) are widely distributed in global arid and semi-arid environment, where high temperature stress is one of the critical environmental factors to control the survival of algae. As a common species in BSCs, Scytonema javanicum appears in alga crust stage as free-living form and in lichen crust as symbiotic form to regu-late the formation and development of BSCs. This study explored the effect of high temperature stress (45℃) on symbio-tic (ss) and free-living S. javanicum (fs). The results showed that high temperature stress declined the photosynthetic activity more dramatically in ss compared with in fs, and high temperature stress induced a higher biomass in ss compared with in fs. Compared with fs, ss had lower growth rate and MDA content, and faster extropolysaccharides-released and soluble protein- to protect from damages. The results showed that, compared with free-living form, the S. javanicum from lichens had higher self-protection efficiency when exposed to high temperature.