Aimed at severe crop water stress over semi-arid region in Northwest China, Some physiological and environmental parameters are observed during the Spring wheat’s flowering and ripe period by CI301-PS photosynthesis instrument，the observation lasts for 1 month. based on the observed value, crop water stress index (CWSI) is calculated, and leaf water potential （LWP）is evaluated. The variations of CWSI, LWP and stomatic conduction with the time and climate change are analyzed. The results show that with the increase of water stress, leaf water will decrease, and CWSI will increase, and leaf water potential will decrease, and stomatic conduction will decrease. As a result, CO2 concentration entering stomata will reduce, and the crop net photosynthesis ratio will decrease, and all of these go against biomass accumulation. By Comparison with these three indexes, it is found that CWSI is the worst index responsing to climate change and crop drought, leaf water potential is better than the stomatic conduction. Because of the reverse humidity in the arid regions, it is the most suitable time to observe leaf water potential and stomatic conduction at 9:00 AM. or after 9:00 AM.