To meet the demand for the integral manufacturing of complex powder hot isostatic pressed (HIP) TA15 titanium alloy components in the aerospace sector, and to address the property matching challenges in dissimilar joining between powder HIP TA15 and forged TA15 alloys, welded joints were fabricated using the tungsten inert gas (TIG) welding process. Furthermore, the microstructural evolution, mechanical property matching, and fracture behaviors of the joints were systematically investigated. The microstructural evolution, mechanical property matching, and fracture behaviors of the joints were systematically investigated. The experimental results indicate that the tensile strength of the welded joint is 999 MPa and the yield strength is 947.3 MPa at room temperature, with a joint efficiency approaching 1.0, indicating that the joint has equal strength to that of the base metals. However, the elongation (10.3%) is approximately 24% lower than that of the powder metallurgy (PM) substrate, with fracture locations randomly distributed on either side of the weld seam. During high-temperature tensile testing at 225 ℃,the tensile strength of the joint is approximately 836.6 MPa, with the ductility increasing by 14.6% compared with that at room temperature, indicating a slight strength reduction with improved ductility. High-temperature stress rupture tests at 500 ℃/470 MPa reveal significant scatter in rupture life (30~60 h), which is only approximately 60% of the base metal's life. All stress rupture failures occur at the weld seam, where the coarse colony boundaries within the weld's Widmanstätten microstructure act as a weak link. Low-cycle fatigue test results indicate that the fatigue life of room-temperature notched samples (Kt=3) reaches 14 167~17 848 cycles, whereas the fatigue life of the samples at 225 ℃ significantly varies (6 133~13 417 cycles), with the fracture location shifting from the weld center to the weld edge. Fracture analysis reveals that room-temperature fracture occurs via a ductile mechanism characterized by large and unevenly distributed dimples. At 225 ℃,the dimples become finer and more uniform, and the activation of dynamic recovery enhances the ductility. High-temperature stress rupture fracture displays a typical “rock-candy” intergranular morphology, with grain boundary α phases acting as crack propagation paths. Furthermore, fatigue fracture results in the initiation of multiple sources, deflected fatigue striations, and final fracture dimples. This study indicates that the microstructural heterogeneity of the joint (the bimodal microstructure of the forging, the Widmanstätten microstructure of the weld, and the basketweave microstructure of the PM substrate) is the fundamental cause of the property mismatch. The coarse colony boundaries within the weld's Widmanst ätten microstructure act as crack initiation sites under cyclic loading, whereas the fine basketweave microstructure on the PM side exhibits superior fatigue resistance.