The present invention discloses a composite hollow plunger structure, which is composed of a plunger rod and a plunger sleeve that are both formed by axisymmetric revolution bodies. An orifice is formed in the central axis of the plunger rod. The plunger rod comprises a bottom end, a shoulder portion, a neck portion, and a ball head. Groove A is formed in a cylindrical surface from the bottom end to the shoulder portion along the whole periphery, while groove B is formed in the inner cylindrical surface of the plunger sleeve; and the plunger rod is integrally connected with the plunger sleeve by means of electron beam welding at the bottom end and the shoulder portion. An electron beam welding method is carried out according to the following steps: (1) machining the two components, namely the plunger rod and the plunger sleeve according to drawing specifications, respectively; (2) soaking the machined plunger rod and plunger sleeve in gasoline for cleaning, and inserting the plunger rod in the sleeve to obtain an assembly to be welded; (3) clamping and loading the assembly to be welded into a furnace; and (4) carrying out electron beam welding. Convenient machining of the composite hollow plunger structure is achieved, which may be completed by a common numerically controlled lathe, and secure and stable welding is realized.