Aiming at the problem that the non-invasive blood pressure measuring instrument is large and inconvenient to carry and needs professional operation, this paper proposes a non-invasive blood pressure measuring system. Based on the principle of pulse wave conduction and the interaction between light and matter, the system extracts and analyses the photoelectric signal modulus of the skin at the wrist. The arterial blood flow velocity is then calculated, that is, the pulse wave conduction velocity. Finally, the hemorrhagic pressure is calculated. We have tested the performance of the system. The experimental results show that the average relative error between the system and traditional blood pressure measuring instruments is less than 5%. The system is helpful to realize real-time blood pressure monitoring. It has the characteristics of small size, low cost, simple measurement method, easy to carry and large data management. It can be used for human health management.