A non-contact brain blood oxygen detecting system includes a mobile terminal device. The mobile terminal device includes a control module, a transmitting module, a receiving module and a display module. The control module is connected to the transmitting module, the receiving module and the display module, respectively. The transmitting module in the mobile terminal device is configured to emit dual-wavelength near-infrared light to a detected subject. The receiving module is configured to receive a light signal after propagation fed back by the detected subject, and to perform data conversion on the received light signal to obtain a digital signal containing blood oxygen information. The control module is configured to obtain the blood oxygen information of the detected subject according to the digital signal obtained by the receiving module. The display module is configured to display the blood oxygen information obtained by the control module.