Abstract: The comparison between the accurate and the approximate expressions of transfer functions of the wind speed and direction errors with balloon coordinate errors sounded by radar is conducted. The suitable range of approximate expression and its correction method are given. The results show that the 701 type radar can not meet in a certain scope the requirement given by WMO about the accuracy of upper wind vector. If the accuracy of angle–measurement is risen to 0.12o, and the accuracy of distance-measurement to 20m, the WMO’s requirement can be basically reached. It is appropriate to use the 5cm or 3cm radar with angle accuracy 0.06o and distance accuracy 10m for some users.