Refractory high-entropy alloys (RHEAs) have great application potential in extreme conditions due to their outstanding high-temperature properties. However, several issues, such as high density, poor room temperature plasticity, and high cost limit their practical application. A new Ti_0.5Zr_1.5NbTa_0.5Sn_0.2 (molar ratio) RHEA with a medium density of approximately 8.0 g/cm³ was prepared to address the aforementioned issues; the effects of heat treatment temperature on the alloy's microstructure and mechanical properties were systematically examined. The findings indicate that as-cast Ti_0.5Zr_1.5NbTa_0.5Sn_0.2 RHEA contains Zr-rich and Ta-rich bcc phases and lath-like Zr₅Sn₃ intermetallics in the crystal. The volume fraction of the Ta-rich bcc phase gradually decreases with the increase in heat treatment temperature, and Zr₅Sn₃ intermetallic first increases and then decreases. The sample presents a near single-phase bcc structure when the heat treatment temperature is 1400^oC. A series of samples have good compressive plastic deformation ability under quasi-static conditions, and the alloy's yield strength increased gradually with an increasing heat treatment temperature. The sample's yield strength quenched at 1400^oC is as high as 1749 MPa. The alloy showed strain rate strengthening effect under dynamic loading, and the yield strength significantly increased. The sample's yield strength quenched at 1400^oC reaches 2750 MPa; however, the plastic deformation ability is reduced. The reason why the strength increases with the heat treatment temperature is that the 9.8% average atomic size difference results in a significant solid solution strengthening effect.