This paper investigates a technique of retrieving three-dimensional wind fields from the dual-Doppler weather radar radial wind which is based on the Cartesian space using variational method. This technology provides a simultaneous resolution of three wind components and satisfies both the minimal dual-equation system and the continuity equation. The main advantage of this method is that it can remove the potential drawback of an iterative solution of Cartesian dual-Doppler analysis techniques which is a major demerit when one retrieves the vertical velocity using mass continuity equation with iterative method. The data pre-processing technology and interpolation are also studied. This work developed a three-dimensional Cressman weighting function to process the interpolation. In order to test the capability and advantage of this method, one numerical experiment based on simulating dual-Doppler radar observations is designed.Firstly, we synthesize the dual-Doppler radar radial velocity and reflectivity from the numerical model Then,the three-dimensional wind components are retrieved from the radial velocity and reflectivity using this technique. The retrieved three-dimensional wind fields are found to be quite consisted with those previously simulated wind fields. Mean difference, root-mean-square error, and relative deviation are defined to test the precision of the method. These statistic errors reveal the accuracy and the advantage of this method. The numerical experiment has definitely testified that this technique can be used to retrieve the three-dimensional wind fields from the radial velocity and reflectivity detected by the real dual-Doppler weather radar.