Abstract: Based on the fact observed in various country, we have analysed the wind speed in valley. The main results are as follows: 1) The relative speed of wind in valley is dependent on.the angle between the wind direction and.the valley as well as the ratio of the width L.of valley to the height H of mountain on both sides of the valley. The wind speed in valley is greater than that in open country when the angle is smaller than 15°-35°, but less than that when β is larger than 15°-35°, In the former condition,, the smaller the angle β and the ratio L/H,the more the wind speed in valley is strenthened, while in the last condition,the larger the β and the sma L/H,the more this wind is diminished. 2)The variation of wind speed with local elevation can be expressed by equation (5).3) The increase of wind velocity with height above the ground can be expressed by equation (6a) except when the wind is strong, in which case equation (7a) should be applied instead. 4) In valley the diurnal course of wind speed near the ground is of double or even multiple maxima. Generally,it's minmum is found in morning and evening, but maximum in afternoon and night.