This paper presents the results of a numerical calculation on the mean behavior of finite length line buoyant jets from slot with width B, discharged perpendicularly into relatively deep cross-flows in the mixing region. The length of diffuser was varied from 4 to 20 times the width of diffuser. The calculations were performed with the standard K-ε model and Hybrid Finite Analytic Method (HFAM) with staggered grid. The phenomenon and development of vortex pairs are simulated successfully and the influence of diffuser length and buoyant on turbulent buoyant jets are analyzed.