An ion generator, a fan coil unit and an air conditioning system. The ion generator includes: a power module; a negative plate connected to the power module; a ground plate spaced apart from a first side of the negative plate, the first side of the negative plate includes a plurality of plasma needles extending toward the ground plate; a positive plate spaced apart from a second side of the negative plate, the positive plate is connected to the power module and has a polarity opposite to that of the negative plate, and the respective sides of the negative plate and the positive plate that are facing toward each other are respectively provided with a plurality of carbon fiber brushes at corresponding positions.