The invention discloses a spectrometer capable of measuring a tiny rotation angle of a collimator, and a measurement method. The spectrometer comprises a pedestal, and the pedestal is fixedly provided with a rotating angle. A telescope, the collimator, an objective table, a first vernier scale, a second vernier scale and a dial are respectively connected with the rotating shaft, and can freely rotate around the rotating shaft without mutual interference. A first screw can enable the telescope to be fixed with the second vernier scale, and a third screw can enable the objective table to be fixed with the dial. A fifth screw can enable the collimator to be fixed with the first vernier scale. Because the collimator can be fixedly connected with the first vernier scale, the first vernier scale and the dial can be used for measurement and reading when the rotation angle of the collimator around the rotating shaft is bigger. When the rotation angle of the collimator is less than one minute and the reading cannot be achieved through the first vernier scale and the dial, the rotation angle alpha of the objective table can be measured through a measurement of the tiny rotation angle of the collimator for calculation and reading.