Abstract: 1.There is a typical phenomenon of mountain-valley breeze in Tianchi. The direction of the moutain breeze is southeast, and the valley breeze northwest, the frequency of mountain breeze is the largest in winter and that of the valley breeze in May and June.2.The velocity of mountain breeze is larger than the valley breeze, this phenomenon is abnormal.3.There are two transitional periods between mountain and valley breezes. The time of occurence of them has a seasonal change, the time of the transitional period from mountain to valley breeze is about three hours later than the sunrise, but from valley to mountain breeze, a little earlier than the sunset.4. The days of mountain-valley breeze in summer is more than in winter.5. After the time of the transitional period (from mountain to valley breeze), the air temperature increses 2-6鈩� and the relative humidity decreses 10-20% suddenly; and from valley to mountain breeze, the air temperature decreses 2-4鈩�, ley, to mountain breeze,the air temperature decrese 2-4鈩�, and the relative humidity increses 15-25% suddenly.6.The wind velocity of mountain valley breeze changes with diurnal range of air temperature, the larger the diurnal range, the larger the wind velocity.