A gravity heat pipe–based two-stage seawater desalination and salt production system, driven by thermal oil, was designed and constructed. Using simulated seawater as the feed solution, the system's water production, energy consumption, efficiency, heat pipe thermal resistance, and equivalent convective heat transfer coefficient were analyzed under varying heat source temperatures prior to the discharge of concentrated brine. The desalination and salt production experiments were conducted at a heat source temperature of 140 °C to enable continuous production of both freshwater and salt. The results show that within the first hour of operation, increasing the heat source temperature leads to higher first- and second-stage water production and efficiency, lower total energy consumption, and higher equivalent convective heat transfer coefficients for both stages. Over extended operation, however, first- and second-stage water production, efficiency, and equivalent convective heat transfer coefficients generally decrease. Once steady-state conditions were reached, the primary and secondary water production rates were 1.08 kg/h and 0.58 kg/h, respectively, while their equivalent convective heat transfer coefficients were 1 240.37 W/(m²·K) and 284.68 W/(m²·K), respectively. Under these conditions, the overall system efficiency was 46.05%, and the corresponding salt production rate was 2.4 g/h.