Abstract: The measurement of normal film characteristic curve is important to choose film system. By means of this process, we can get ISO speed, ISO average gradient and ISO gradients G2 and G4. These parameters are significant indicator for film manufacturers to ensure product quality and for users to know the product property. The measurement method of normal film characteristic curve is realized by working out ray energy value(units: Gy) through keeping tube current, tube voltage and exposure time fixed and uniformly changing focus-to-film distance. At last, we can get the photographic characteristic parameters of the film.