In order to research the influence rule of solution temperature above β transformation temperature on the microstructural parameters and mechanical properties of Ti-55531 alloy, series heat treatments, OM, SEM and tensile testing methods were carried out. Results indicate that all microstructures of the alloy consist of lamellar α_s, residual β laths and a few grain boundary α after solution at different temperatures in β phase region and aging treatment. Different solution temperature affects the original β grain size of Ti-55531 alloy, and then the content and size of aging precipitated α_s phase, which ultimately results in mechanical properties of the alloy. When the solution temperature is ranging from 830 ℃ and 900 ℃, with the increase of solution temperature, the size of original β grain increases, and the length, width and length-width ratio of α_s phase precipitated by subsequent aging increase at first and then decrease. Meanwhile, the volume fraction of α_s phase increases, the strength of the alloy gradually decreases, and the plasticity decreases first and then increases. As the solution temperature is 860 ℃, the alloy could obtain the good cooperation between strength and plasticity. Fracture mode of lamellar microstructures is a mixed mode, including microvoids accumulation, transgranular cleavage and intergranular fracture.