Based on the model of multilayered biological tissue, a method to measure tissue oxygenation saturation by using noninvasive near infrared spectroscopy was present. For the subjects with different constructions and scales of their overlaying tissue, the correction method which make results reliable and comparable in semi quantitative measuring change in tissue blood oxygenation was proposed. A new compact monitoring instrument which includes a probe with a dual wavelength LED and two integrated optical detectors at different distance from light source was designed and developed. During the ischaemia of forearm induced by 240mmHg pressure with inflating cuff, the result of concentration changes in oxyhemoglobin, deoxyhemoglobin and the value of tSO 2 is consistent with the foreign reports by TRS methods. It shows that the monitoring system is very stable and feasible.