Tantalum(Ta)/Molybdenum(Mo) dissimilar joint was successfully joined by laser welding process with pure Pt filler wire. The weld surface morphology, microstructure, interface element distribution, fracture morphology, phase structure, electrical performance and environment adaptability were studied by metallography microscope, scanning electron microscopy, hardness and mechanical properties of joints, X-ray diffraction, electron micro-hardness and tensile test, vibrationStable and ultra-high high vacuum system. Laser parameters have profound effects on microstructures of the laser-welded joints. Pores were generated in the weld zone caused by the preferential vaporization of pure Pt filler metal. The weld zone mainly contained TaPt2, TaPt3 and MoPt phase, resulting higher hardness in the weld zone than that of base metal. The joint fracture surface exhibited typical brittle fracture morphology. The electrical property and vibration test had examined the joints welding quality for electron guns. Meanwhile, the reliability of laser welding process in the development, production, and application of microwave tubes had been verified.