The invention discloses a powder coating machine of a lamp tube. The powder coating machine comprises a rack; a rotating plate for conveying lamp tubes and ovens for baking lamp tubes are arranged inside the rack; upper slots and lower slots that correspond to each other are distributed at the upper edge and the lower edge of the rotating plate along a circumferential direction; and two ends of lamp tubes penetrate the upper slots and the lower slots respectively. In addition, the rack is also provided with a coating device having upper joints and lower joints; the upper joints are used for coating fluorescent powder on lamp tubes and the lower joints are used for recycling the fluorescent powder; and the upper joints and the lower joints are embedded into the two ends of the lamp tubes upward and downward and rotate back and forth in an axial direction until coating is done uniformly. According to the invention, because the upper joints and the lower joints are embedded into the two ends of the lamp tubes upward and downward and rotate back and forth in an axial direction, lamp tubes are coated uniformly, so that a phenomenon of non-uniform thicknesses of fluorescent powder is avoided.