Based on wind data of 16 meteorological stations in north part of Shaanxi province, by using power function, successive regression, K.Pearson Ⅲ type and curve fitting, the extreme value of maximum wind speed was estimated for 300kv high pressure transmission line from Yulin to Shenmu, which happened every 15 years at 15m above the ground. And the design value of maximum wind speed was finally suggested to be 30m·s^-1.