Abstract: Two years field experiment shows that in semi-arid region of loess plateau, the critical period of limited irrigation for spring wheat field is from 3 leaves stage to boot stage, but owing to high variability of rainfall in the region, the critical period and the effect of increasing yield in various year types of precipitation are different and actual critical period did not coincided with physiological one.The countermeasures for limited irrigation in semi-arid region and water consumption and yield formation processes are discussed in this paper.

Key words: Semi-arid region, Spring wheat, Limited irrigation, vapor pressure deficit, abscised measurement, maximum net photosynthetic rate, Larix olgensis.