This paper used ammonia-water as the working fluid to conduct the experimental investigation on an ocean thermal energy conversion (OTEC) system. A test bench was built to study the performance of the lab-based OTEC system under different operating conditions and a horizontal tubular rising-film generator was used. Besides, an orthogonal analysis was conducted to assess the impacts of heating and cooling source temperature, as well as the solution flow rate on the performance of test bench. The results show that the heating source temperature has the most significant effects on the thermal efficiency, followed by the cooling source temperature. In contrast, the solution flow rate has little impact on the thermal efficiency. Also, higher heating source temperature leads to a relatively higher thermal efficiency. Moreover, the value of thermal efficiency with heating source of 30–40 °C and cooling source of 5–15 °C is 0–0.75%. The heat transfer temperature difference exists in generator and absorber restricts the performance improvement of the reheat power cycle.