Abstract: By using the site-specific observation data of oil flax growth and related meteorological records in semi-arid region of Loess Plateau, this paper studied the effects of climate change on the oil flax growth, and analyzed the relationships between the oil flax water use efficiency and meteorological condition. In this region, the annual precipitation displayed a decreasing trend, and its climatic trend rate was -15.80 mm·(10 a)^-1, with an annual periodic change of 3 a and 6 a, whereas the annual air temperature had an increasing trend, and its climatic trend rate was 0.36 ℃·(10 a)^-1. In crop growth period, the aridity index displayed a marked increasing trend, its climatic trend rate was 0.12·(10 a)^-1, and the aridity tendency was more obvious from the beginning of 1990s to the year 2009. From sowing to maturation, oil flax needed 120-150 d, 1700-2100 ℃·d of ≥0 ℃ accumulated temperature, 200-250 mm precipitation, and 1000-1300 h sunshine hours. The main meteorological factors affecting the oil flax growth in the region were air temperature and precipitation. The increase of air temperature shortened the prophase vegetative growth stage, whereas the increase of air temperature and the decrease of precipitation extended the reproductive growth stage, causing the extension of the whole growth period of the oil flax. The air temperature in the oil flax whole growth period except at seeding stage and maturing stage had negative effect on the yield formation, being more obvious at squaring stage, whereas the precipitation in the whole growth period except at blooming stage had positive effect on the yield formation, being more obvious at seeding stage. The water use efficiency of the oil flax was significantly positively correlated with the air temperature and sunshine hours at seeding stage as well as the aridity index from squaring stage to maturing stage, and negatively correlated with the precipitation from squaring stage to maturing stage. In the study region, the aridity index from May to July was the key factor affecting the water use efficiency of oil flax.