A new method is presented here for solving three-dimensional velocity field of a turbulent jet in a cross flow. Taking curvilinear coordinate system in order to fit the jet better, we assume that the second order partial derivetives along the jet axis can be neglected, and the pressure axis gradient of a point in a cross section can be replaced by the axis gradient of the average pressure over this cross section, thus the basic equations become parabolic. We can solve these equations section after section, i. c. we reduce a three-dimensional problem to a series of two-dimensional problems. It makes the a mount of computations decreased greatly, and all computations can be accomplished in a micro-computer. This method is applicable for the case in which the cross wind is not strong.