A light source sensing device and a light source sensing method thereof are provided. The light source sensing device includes an optical sensor, a rod, a motor and a controller. The optical sensor is used for sensing lighting brightness emitted by the light source. The rod is disposed on a circular track which surrounds the optical sensor. When the light source irradiates the rod, a shadow is formed on a sensing surface of the optical sensor. The motor drives the rod to move along the circular track in a moving speed. The controller is coupled to the motor and the optical sensor, and controls the optical sensor to sample in a sampling frequency during a sampling period for obtaining a plurality of brightness values. The controller calculates and processes the brightness values for obtaining an irradiating angle of the light source.