The near field stability and mixing characteristics of buoyant jets produced by thermal diffuse in quiescent shallow water are investigated numerically to predict under what combinations of discharge and ambient characteristics the near field will be stable or unstable.Analyses for different discharging types show that the discharge stability is purely dependent on the near-field behavior of the jets, or the dynamic interaction of the buoyant jet region, the surface impingement region and the intal hydraulic jump region, and is independent of the far-field geometry of the receiving water.The stability criterion is a function of the relative submerged depth, and source densimetric Froude number.