Abstract: Investigation on the effects of temperature and water stress on leaf water and osmotic potentials of spring wheat and maize was conducted under the condition of laboratory．The results show that at a fixed temperature．the leaf water potentials are down in trend with soil water potential decreasing；at the same soil potential，the leaf water potentials down in trend with temperature increasing．When the temperature rises and the water stress becomes bigger，the leaf osmotic potentials show down first and then up．Though the comparison between leaf water and osmotic potentials changes，the accommodation osmotic power of wheat are higher than that of maize．From the idea of energy，crops grow best at 27℃ by analysis of △G、△S、△H.