Detecting apparatus and detecting method thereof

A detecting apparatus for detecting an object includes at least a screen, at least a detecting unit and at least one holding unit. The screen is partial light-permeable and has a first surface and an opposite second surface. The object is disposed adjacent to the first surface of the screen. The detecting unit is disposed correspond to the object and disposed adjacent to the second surface of the screen. The holding unit holds the three relative distances between the screen, the light-emitting and the measuring unit. The detecting unit captures the image of the second surface of the screen so as to calculate the optical field distribution of the object. The detecting apparatus of the invention can measure the optical field distribution of a light source quickly and has the advantages of low cost and high accuracy.