The sub-stable β-type TB18 titanium alloy exhibits a significant strengthening effect through solutionizing-ageing and possesses excellent potential for achieving a balanced combination of strength and toughness. As a result, it has emerged as a favoured material for manufacturing high-end aviation components. This work aimed to investigate the impact of solid solution treatment on the microstructure and mechanical properties of TB18 titanium alloy. Specifically, the effects of different solution temperatures, solution times, and slow cooling rates after solutionizing on the alloy"s microstructure and mechanical properties were illustrated. The goal is to understand the mechanism behind the interaction between solution treatment and the microstructure-mechanical properties of TB18 titanium alloy. The results indicated that following the solutionizing and aging treatment within the β single-phase region, lamellar and needle-like αs phases precipitated within the β matrix. The presence of lamellar αs phases contributed to the improvement of the toughness of the TB18 titanium alloy. Furthermore, it was observed that the fracture toughness of the TB18 titanium alloy improved with an increase in the thickness of the lamellar αsphases. Elevated solutionizing temperature or prolonged solid solution holding time can result in the coarsening of β grains in TB18 titanium alloy, leading to a decrease in material strength and plasticity. When increasing the cooling rate from 0.25 ℃/min to 1 ℃/min after solutionizing, the fine α_s phases uniformly distributed within the TB18 titanium alloy after aging treatment, and the tensile strength increased to 1343 MPa while the elongation was 5 %. By subjecting the TB18 titanium alloy to a solutionizing regime at a temperature of 870 ℃ for 2 hours, followed by air cooling, it achieved a favorable combination of strength and toughness. Further aging at 530 ℃ for 4 hours, again with air cooling, results in a tensile strength of 1315 MPa, yield strength of 1225 MPa, elongation of 8.5%, impact toughness of 29.2 J/cm2, and fracture toughness value of 88.4 MPa . m1/2.