Abstract: The temperatures are observed with HOBO PRO SERIES instrument in plastic greenhouses in winter．The relation of temperatures between inside and outside of plastic greenhouse has been discussed on the above base．When the outside temperatures are 10℃ and 15℃ respectively，the temperatures in the greenhouse correspond to 7．5℃ and 16℃ ．The lowest temperature is evaluated，the ending time of lowest temperature is made statistically and the speeds of rising and dropping temperatures are recorded too．The persistent time of the lowest temperature in the greenhouse is 106 minutes at an average，ending at 6：40～8：20 under a clear weather，and is 135 minutes．ending at 6：50～9：00 under an over．cast weather．The time when the temperature rises to 10℃ is at 10：30 under a clear weather，and at 10：40 under an overcast weather．The time when the temperature drops to 10℃ is at 16：00 under a clear weather，and at 16：00～ 19：00 under an overcast weather．