The invention relates to a sleep and breath preliminary screening instrument with a timing power-on function and a power-saving method. The instrument comprises a casing wearing on the wrist, a display and control buttons are arranged on the casing, a nose airflow signal input interface and a blood oxygen signal input interface are arranged on the side wall of the casing respectively, and a control analysis circuit is fixed in the casing. According to the instrument, the timing power-on is achieved under a state that the circuit is completely out of power, cruising time of a battery is guaranteed, the power-on can be identified automatically, the effectiveness of the power-on state can be determined, and ordered carrying out of manual power-on and timing power-on can be achieved. The instrument is in a power-saving mode during storage, the working current is smaller than 30mA, the instrument can perform data storage as long as 20 hours, and the screen is in a blank screen state during the power-saving mode, so that the visual trouble caused by bright screen of the instrument during sleep of a patient can be avoided.