考虑熔池蒸气反冲压力、表面张力、热浮力等力学因素和熔池内、外部的对流、辐射等热学过程，采用沿深度方向衰减的旋转高斯体热源简化熔池对激光的吸收，采用流体体积法追踪气/液界面，采用液相体积分数法和焓-孔隙度法分别处理熔化凝固潜热及液-固糊状区的动量损失，建立了激光深熔焊接熔池的三维瞬态模型。运用该数学模型获得了不锈钢激光深熔焊接过程中熔池及小孔温度场和流场的瞬态变化。计算表明，熔池最高温度呈现线性增长、趋于平稳和小幅振荡三个阶段；小孔在焊接过程中呈现前倾和后倾两种姿态，且存在周期性振荡行为。计算得到的熔池形状和焊缝横截面的试验结果基本吻合，小孔振荡行为也从相关文献的实验结果中得到了验证。

We set up the three-dimensional transient model of laser deep welding considering the mechanical factors such as evaporative recoil back pressure, the surface tension, the thermal buoyancy and the thermal parameters such as the convection and radiation in and out of pool. In the model, the rotary Gauss body heat source attenuation along depth direction was applied to solving the laser absorption of molten pool, the volume of fluid method was adopted to realize the tracking of gas-liquid interface, and the liquid volume fraction method and enthalpy-porosity technique were used to compute the latent heat of molten metal solidification and the momentum loss in the liquid-solid mush zone. Then the transient temperature and flow field of pool and keyhole were obtained in the laser deep penetration welding of stainless steel with this numerical model. The results show that there are three stages for the maximum temperature in the welding, which are the linear growth, the tending to stable and the small oscillation, and there are two kinds of keyhole orientations, forward and backward, and there is periodic oscillation for keyhole in the welding. The simulation results of final weld formation agree with experimental data of weld cross section well, and the oscillatory behavior of keyhole is also verified by relevant references.