Abstract: The values of the photosynthesis rate (Pn), transpiration rate (Tr) and water utilization efficiency (WUE) of Armeniaca sibirica plantation growing in the agriculture and grazing ecotone area in the north Loess Plateau in the growing season were measured with Li6400 portable photosynthesis system, and the major influencing factors related to the change of these physiological indexes were discussed. The results showed that the light compensation points (LCP) in leaves of the A. sibirica plantation changed from 15.33 to 53.91 μmol/(m2·s) in different period of time, the light saturation points (LSP) varied from 1159.38 to 138233 μmol/(m2·s) and the apparent photon utilization efficiency (Φ) varied from 0.0258 to 0.0464 in the growing season. The CO2 compensation point (CCP) of A. sibirica plantation changed from 48.97 to 89.38 μmol/mol, the CO2 saturation points (CSP) varied from 32220 to 41337μmol/mol, indicating that A. sibirica was a heliophilous tree species that was not shade tolerant and should be planted on sunny sites. The Tr value of the A. sibirica plantation in different months dropped in the order as Aug > May > Jun > Jul; while the WUE value dropped in the order as Jul > Jun > Aug > May in the growing season in the studied area.