Abstract: X-ray security machine has low recognition accuracy in the field of liquid identification because of the inaccurate location and the influence of containers. Based on X-ray transmission, this paper proposes a liquid recognition method based on dual-energy X-ray security machine in an ideal state. It can obtain accurate container location by high and low energy image and use SVM and LR to realize recognition by calculating the effective atomic number. Finally, the availability of the algorithm was verfied by simulation and experiment.