Abstract: Taking the reverse design of impeller and diffuser blades of a diffuser mixed flow reactor coolant pump as the objective, an approach to acquire the complete geometric data of the blades system was explored by using combination with forward engineering on condition that impeller and diffuser are not be broken. To modify and control 3D surfaces preliminary geometric model was reconstructed through streamline-wise parameter curves with blade digital design from the incomplete blade data, and then the full pump flow passage is established by combining the preliminary model of blade system with the other flow parts. The external characteristic curves of the pump was predicted by 3D flows simulation inside the complete pump passage under operating discharge range from 0.2Q_d to 1.2Q_d, and then the accuracy of the reverse design 3D surfaces of blades system was evaluated by comparing the predicted and the original tested external characteristic curves. It has demonstrated that the presented approach can ensure the required accuracy and satisfy the needs of the reverse design of impeller and diffuser blades of a mixed flow pump.