The way to implement virtual teaching of the largescale structure nonstandard welding machine was studied. The system model of hydraulic support horizontal seam welding machine was set up in CATIA, and then analyzed its kinematic chain composing, established its kinematics equation, and given its calculation method and results. Then its true virtual special machine was set up in DELMIA, the welding trajectory planning and teaching were carried out on the basis of hydraulic support welding process, finally the welding track without interference was created. The virtual simulation of hydraulic support horizontal seam welding is completed, which provides work instruction for the onsite debugging of the actual equipment.