The present invention provides a high-dynamic-range sensing device and the sensing method thereof. The high-dynamic-range sensing device includes a control unit and sensing units with different sensing ranges. In the sensing method, the sensing units give sensing values, and then the control unit compares the sensing values and the upper sensing limit of the sensing units, respectively. When a sensing value is equal to the upper sensing limit, the control unit rejects the sensing value or interrupts the sensing of the sensing unit thereof. Thereby, the sensing device quickly excludes the sensing units which obtain saturated signals and their sensing values and thus switches between the alternative sensing units with different sensing ranges or picks up the optimum one of the sensing values.