Neutral beam injection (NBI) is one of the most effective tools of four auxiliary plasma heating methods for fusion plasma heating and current drive. Now, a next generation fusion device, China Fusion Engineering Test Reactor, is under design, and a large negative NBI is foreseen. In order to demonstrate the key technology and performance of a negative ion source, a negative radio frequency (RF) ion source test facility has been developed since 2017 in the Institute of Plasma Physics, Chinese Academy of Science. A prototype RF ion source with double drivers (having the same structure with an inner diameter of 200 mm) was developed and tested on the test facility to preresearch the key technology of the RF plasma generator. The driver is equipped with a water-cooled Faraday shield to protect the alumina cylinder from the plasma, and the plasma expands into the rectangular expansion chamber. The RF power of 100 kW with a frequency of 1 MHz is transferred to the RF driver by a matching unit. The characteristics of plasma discharge were studied with classical diagnostic tools, such as the Langmuir probe and water flow calorimeter. Based on the plasma performance tests, a high power of 82 kW plasma discharge for a long pulse of 1000 s was achieved. In this paper, the details of the ion source design, characteristics of plasma, and future research plan will be presented.