Abstract: In order to meet the high-quality connection requirements of stainless steel and tantalum in the cathode assembly of the electric propulsion system, a laser welding experimental study was carried out. The result shows that within the range of offsets commonly used in laser welding, the cross-section of the joint is in the brazing forming mode, and the weld is composed of solid solution and eutectic structure. If most of the beam irradiates tantalum, or the beam is not biased towards tantalum but the power is high, the amount of melting of the tantalum base metal will increase, and its fusion into the weld will generate a clear brittle intermetallic compound layer, which is unavoidable between layers and in layers. Therefore, the optimal energy mode is: the center of the laser beam does not shift to tantalum, and at the same time, the laser power is reduced as much as possible under the premise of ensuring the penetration depth, and the welding speed is correspondingly reduced. The interface layer is a structure in which a variety of compounds are generally distributed in layers. The longitudinal cracks of thick-layer joints are mostly born in the compound layer with the worst bonding force. The test results show that the weakest layer is between μ(FeTa) and ε(Fe2Ta). The cracks of thin-layer joints mostly originate between the compound layer and the eutectic structure, but the propagation directions are different.