The present invention relates to a last substrate sensing device used for a substrate decomposition equipment and an adjusting method, the sensing device comprises a support reality, a sensor opticalfiber testing head used for sensing signals, a condenser lens, a splint and a substrate limit column; wherein, the splint is arranged in parallel under the resistive substrate to be decomposed and isconnected with a rise-drop mechanism of the substrate decomposition equipment; the substrate limit columns are vertically arranged in the four corners on the upper surface of the splint; the verticalstrutting part of the support reality is a rectangular strip, the upper end that is vertical to the strutting part extends horizontally and forms a crossbeam of the optical fiber testing head of a positioning sensor; the parallel substrate limit columns of the support reality are arranged at one side of the splint and positioned to connect with the soleplate of the substrate decomposition equipment; two sensor optical fiber testing heads are arranged respectively above and under the corresponding resistive substrate on the crossbeam of the support reality, and the front end of the resistive substrate is provided with the condenser lens. The device is adopted for positioning adjustment and accurate feed-back of the information about the position of the last substrate via the sensor opticalfiber testing head when the resistive substrate is moved.