In this paper, microstructures of 316L austenitic stainless steel joints subjected to 0 mT and 18 mT longitudinal magnetic fields were studied. The change of morphology and texture of austenite (γ) and ferrite (δ) phases were primarily analyzed concerning fused line, columnar zone and central zone. When the magnetic field intensity was change from 0mT to 18mT, the upper hybrid welding layer changed from “T shape” to “triangle shape”, accelerating the heat transfer instead of the heat convergence in the heat affected zone and increasing the temperature gradient of the solid/liquid front. At the fusion line, the addition of magnetic field changed the growth direction of δ phase from ［1 0 0］to ［2 0 3］, deviating from the normal direction of fusion line (［1 0 0］) And the crystal texture changed from (0 1 6)［21 0］to (2 3 3)［32 0］. However, the increase of temperature gradient led to the concentration of ［1 0 0］crystal direction distribution. In the columnar zone, the addition of magnetic field altered the growth direction of δ phase from ［1 0 0］to ［2 1 2］, also deviating from the theoretical temperature gradient direction (［1 0 0］). And the crystal texture changed from (0 3 1)［91 3］to (3 10 2)［21 2］with the increased fraction of the special δ/γ orientation relationships. In the central zone, the growth direction of δ phase was changed from ［1 0 5］to ［1 0 3］and gradually deviated from the theoretical temperature gradient direction (［0 0 1］) with the addition of magnetic field. And the crystal texture was altered from (1 0 0)［01 5］to (1 0 0)［0 3 1］with a reduced fraction of the special δ/γ orientation relationships.