As the biggest single dish radio telescope in the world, FAST would significantly improve the capability of current VLBI networks below 3 GHz. There are several VLBI networks, such as CVN, EVN and LBA, are suitable for FAST to join, after considering the location of stations and frequency of receivers. FAST would mainly contribute sensitive long baselines to the current VLBI networks, which would benefit the research in need of high resolution and high sensitivity. The slewing speed of FAST is not high. In order to effectively join the phase-referencing observations, selection of nearby calibrator or a new small antenna could be the solution.Very Long Baseline Interference (VLBI) is one of the topic sciences of the Five-hundred-meter Aperture Spherical radio Telescope (FAST), which would provide significant contribution to the current VLBI networks. In order to make use of the significant contribution of FAST to the VLBI observations, it is necessary to pick suitable VLBI research projects. We summarize their main VLBI projects of three mega radio telescopes with hundred-meter aperture and give some suitable VLBI projects for FAST. FAST VLBI system consists of time/frequency system, the data sampling terminal and the data reservation system, which are all state of the art. Two fringe experiments were conducted and the first VLBI fringe between FAST and Tianma telescope was introduced. Future plans, including suitable VLBI networks to join, are discussed. Six suitable VLBI research projects are selected for FAST. The first VLBI fringe was achieved between FAST and Tianma telescope. VLBI networks, such as CVN, EVN, and LBA are suitable for FAST to contribute its significant sensitivity. Nearby small antenna could help FAST to join the phase referencing observations.