A depth sensing system and a depth sensing method are provided. The sensing system includes depth sensing module and a processor for performing the sensing method. The depth sensing method incudes: obtaining a sensed target data set via a depth sensing module; calculating a period number corresponding to a measuring pixel; and calculating an actual range value or an actual depth of the measuring pixel in accordance with a period number and a range value of the measuring pixel. The step of calculating the period number of the target data set includes: calculating a spatial ratio in accordance with the position values of the pixel of optical center and measuring pixel, and a focal length of the depth sensing module; calculating a basic range in accordance with the spatial ratio and an unit depth; and calculating the period number corresponding to the measuring pixel.