A series of polypropylene-g-poly(ethylene-co-1-butene) (PP-g-EBR) graft copolymers with well-defined long chain branched (LCB) molecular structures were synthesized via the combination of coordination polymerization and anionic polymerization. The structure property relationships of PP-g-EBR were systematically investigated. The structural information was clarified by characterization of H-1 NMR and SEC equipped with triple detectors. The DMA measurements demonstrated that the amorphous EBR branches were miscible with the PP backbones. The melt behavior of the PP-g-EBRs was studied with small-amplitude dynamic rheological measurements. Increasing branch length and branch density both led to increased zero-shear viscosity, more pronounced shear-thinning behavior, elevated value of storage modulus at low shear frequencies, more significant upshift deviation from linear behavior in the Han plot, and reduced loss angle. Comparatively, branch length contributed more to the improvement of rheological properties than branch density did. Interestingly, DSC results showed that the crystallization temperature of PP-g-EBR increased with the enhancement of branch length and branch density; however, when the LCB level exceeded a certain degree, further increasing the LCB level would reduce the crystallization temperature.