Abstract: In an apparatus for quantifying the amount of evaporation deposition of a solid substance and its method, the apparatus is connected to a reaction chamber, and a solid substance to be evaporated, a heating source and a load cell are disposed in a heating chamber. The load cell is for detecting the weight of the solid substance, and the reduced weight of the solid substance to be evaporated per unit time is equal to the mass flow of the reaction gas, so that the status of the reaction gas can be known by the weight simultaneously. When the solid substance is heated to a state to form the reaction gas, the heating chamber reaches a saturated vapor pressure greater than a vacuum background pressure of the reaction chamber, the reaction gas continues to flow along the pipeline stably towards the reaction chamber to manufacture a thin film.