Abstract: Based on observed meteorological data for 30 years in Yan'an district, the temperature both inside and outside the greenhouse during strong temperature drop process was compared. It is concluded that the thermophilous crops planted in the greenhouse would be damaged, when the air temperature dropped to -20 outside the greenhouse and the temperature would be under 0inside the greenhouse, even though the protection measures were adopted. Taking -20as a critical temperature at which the plant freezing injury would occur, the freezing zone was divided in the Yan'an district. The different forecast service patterns were put forward according to the air circulation status.

Key words: Freezing injury weather, Freezing injury weather, Analysis, Forecast, Yan'an