The three components of wind velocity at the horizontal angle and wind directions of three kinds of ultra sonic anemometers were measured when the wind blows from respective 30 degrees in the experiment. The stems of errors between theoretical data and measured data of each wind velocity component and between accurate data and measured data of wind direction were analyzed. Their correction methods were presented and verified. The results are as follows: 1) The extent'of errors of wind velocity components were 30-40% in maximum which were arisen by probes and their supporting and were 10% or 40% or 50% by supporting posts. 2) The extent of errors of wind directions were within 4° or 6°. 3) The correction methods of wind velocity at the horizontal angle and wind directions were presented by using quadratic equations in respective wind direction extents and were verified.