Disclosed a passive wireless sensor for detecting discrete droplets and bubbles. A first inductor channel and a second inductor channel are disposed opposite each other to form a capacitor channel, the first inductor channel is connected to the second inductor channel to form a resonant circuit. When a detection object passes through the detection channel, the permittivity between the first inductor channel and the second inductor channel changes and consequently a capacitance value of the capacitor channel changes, thus resulting in a change in resonant frequency of the resonant circuit. A readout device is used to read the resonant frequency of the resonant circuit and perform detection according to the resonant frequency to obtain information of a corresponding detection object.