Abstract: Taking the variety “mid-night” as the CK ,Variation of several physiological indices including the lethal temperature,membrane permeability,proline accumulation and malondia1dehyde of four grasses under h- igh temperature stress was measured. The result showed that the lethal temperature of P. pratensis L.、P. spho- ndy lodes Trin.、P.annua L.、P.angustifolia.L. and “midnight” was 56.56℃、55.95℃、52.88℃、53.78℃、和56.09℃respectively ; cell membrane permeability and the content of malondia1dehyde raised, proline accu- mulation were gradually increaset then decreased with the temperature grades going up. It was found that there existed some difference of heat resistance among the four grasses. The ranks of heat resistance of four grasses were P. pratensis L.、P. sphondy lodes Trin.、P.annua L.and P.angustifolia.L..