The SAW delay-line sensor can obtain the energy of the RF pulse query signal through the wireless method. The RF pulse echo signal of the SAW delay-line sensor is significant effected by the different query pulse width of the RF pulse query signal, which is directly related to the sensor precision. The size of the IDT and reflectors, the distance between the IDT and reflector, and the distance among the different reflectors can affect the selection of the RF pulse query signal. The selection method of the query pulse width is discussed through the theoretical analysis and experimental analysis according to the SAW delay-line transmission characteristics. The query pulse width can be calculated directly through the design parameters of the SAW sensor.