There is provided a detection device using a SPAD array including a sensor array, multiple counters, a processor and a frame buffer. The sensor array includes a plurality of SPADs respectively generates an avalanche current while receiving a photon. Each counter counts a number of triggering times of the avalanche current of a corresponding SPAD within an exposure interval. The frame buffer is pre-stored with a plurality of gain calibration values corresponding to every SPAD of the sensor array. The processor accesses the gain calibration values to accordingly calibrate a counting image frame outputted by the sensor array to output a calibrated image frame.