Abstract: Analysis the effects of temperature on apple flowering time by using apple phenology and meteorological data of Luochuan county and Ansai district of Yan’an city for many years to improve the level of weather forecast of apple flowering period. The results show that the apple initial flowering day in Yan’an is in mid-to-late April, and the difference between North and South is about 10 days. The initial flowering day of apple can vary by 15 days between years in the same area. The date and the accumulated temperature to steadily passed 3 ℃,10 ℃ are similar in Luochuan county and Ansai district, which are suitable for analyzing apple flowering period. Within 48 hours, the minimum temperature decrease by more than 8 ℃, and the weather with minimum temperature ≤4 ℃ is determined to be a severe cooling process. A cooling weather could delay the flowering period by 3~6 d. The weather process is identified as flower forcing high temperature process, when the temperatures averaging above 15 ℃ for more than 10 days, higher than the average annual temperature of 4 ℃ or above. High temperatures can prompt apples to bloom 5 days earlier. In order to predict the flowering period of apple by accumulated temperature, we should pay attention to the accumulation process of stable passage through 3 ℃, 10 ℃ date and accumulated temperature, and severe cooling and high temperature weather, which have obvious influence on flowering period.

Key words: temperature fluctuations, apple flowering period, accumulated temperature, Luochuan county, Ansai district