An auto-fill two-layer two-half wear resistant elbow of a concrete pump truck consists of an outer-layer protection elbow, an inner-layer heterogeneous wear resistant combined elbow and a wear resistant connecting flange. A filling space is provided between the outer-layer protection elbow and the inner-layer heterogeneous wear resistant combined elbow. The wear resistant elbow is designed as a two-layer two-half unique structure including a protection layer and a wear resistant layer. Upon using the wear resistant elbow for the first time, the concrete grout fills the reserved slit via the heterogenous combined elbow and enters the reserved filling space, allowing the outer-layer protection elbow and the inner-layer heterogeneous wear resistant combined elbow to be fixed as a whole.