Abstract: Aim To study a real time traffic flow measurement system providing necessary statistics of traffic flow parameters for traffic departments through measuring vehicle number, velocity and other traffic parameters.Methods\ The real time traffic flow measurement was processed through image difference method. Because of its capability for data processing at high speed, the RISC (reduced instruction set computer) was used to carry out real time and practical research on the whole system. Results\ Experiment devices of real time traffic flow measurement was developed and the practical algorithm of image processing was designed and debugged. Conclusion\ In practical traffic flow measurement, the precision of measuring vehicle number is over 95%. The system work robustly under various conditions, it can automatically cope with the gradual and sudden changes of the environment light.