A method to obtain three-dimensional (3D) trajectory of moving target through single X-ray source imaging is presented. 3D trajectories of moving objects are obtained through target detection, stereo matching and 3D reconstruction based on the digital radiography image array collected. Compared with common approach of multi-view imaging, this method has advantages of simple device and equivalent accuracy. Simulation shows the validity and stability of the proposed method. The error analysis of 3D trajectory measuring result is also given. It turns out that the measuring error is related to the detector resolution and target size.