The Comprehensive Research Facility for Fusion Technology (CRAFT) is a national large research infrastructure in China. CRAFT aims to develop the key technologies for future fusion reactor and the negative ion source neutral beam injection (NNBI) is one of the test facilities or prototypes. CRAFT NNBI test facility mainly includes two test stands and several shared supporting systems. One is the Hefei Open-facility for Negative-ion Source Research, which is devoted to the experimental study of the negative ion source. Other one is the Chinese Fusion Engineering Testing Reactor Advance Neutral Beam Equipment, which acts as the prototype of the neutral beam injector for Chinese Fusion Engineering Test Reactor. Under the CRAFT project, the single-drive, the dual-drive, and the quad-drive RF negative ion sources have been developed and tested step by step. The associated CRAFT NNBI Physics Activity was established to carry out synergistic study of key issues of NNBI technology. Since the experimental research starting in 2021, the achieved parameters of the CRAFT NNBI, such as the negative ion beam energy, beam power and pulse duration, have been steadily improved. At present, based on the dual-drive RF negative ion source with single-stage accelerator, the negative hydrogen ion beams with the beam energy of >200 keV, beam power of >2 MW, and pulse duration of >100 s have been attained repeatedly. Simultaneously, several accompanying experimental research can give support to the future improvements of the CRAFT NNBI in terms of the RF coupling frequency, plasma uniformity, Cs injection, beam divergence, high voltage holding, neutralization efficiency.