The blood oxygen saturation is a very important physiological index in common clinical diagnosis and family care. The patient’s life is related to the level of blood oxygen saturation to some extent, so the oxygen saturation should be detected in the clinical, especially in the operation. Because monitoring the volatility of the blood oxygen saturation plays an important role in the prevention and treatment of the pulmonary heart disease, it has the extremely vital significance. The SpO2 system which we designed is based on AFE4400 and we developed an application of android smartphone in order to display the PPG signal and the blood oxygen saturation timely and exactly. It’s easy to use and makes a further cost reductions. The experimental results show that the system has a very high accuracy.