Brain blood-oxygen detecting use dual wavelenght near infrared light,760nm and 850nm,which can noninvasively,real-time,continuously monitor brain blood-oxygen information.Firstly，the dual wavelenth math and physics model was deduced，and this model need only measure one parameter which is light intension absorption rate n.Secondly,the wavelengths and source-target distance were choosed.At last,the experiment of holding one′s breath proved the validity of the method.