The present invention discloses a method for measuring dental cavity diameter by utilizing artificial intelligence technique and fiber optic displacement sensor. The method comprising steps of constructing a fiber optic displacement sensor, FODS scanning and imaging system; acquiring teeth image by using the FODS scanning and imaging system; performing cavity localization process by determining the exact location of the cavity in the teeth image; extracting the first and second features by performing feature extraction process; performing fuzzy logic on the second feature; and performing classification process on the reflected signals by a single-layer perceptron, SLP network.