Polylactic acid (PLA) has good renewability, biodegradability, biocompatibility and thermo-mechanical properties, which make it one of the best polymeric substitutes with many potential industrial applications. However, PLA suffers from low rate of crystallization, melt strength and short relaxation time, which limited its application and processing in molten state. Grafting from (GF) and grafting to (GT) are two main methods to prepare surface modified polymers with PLLA chain. We put forward a novel modification combining GT and GF methods to synthesize comb-like NCC-g-PLA as macromolecular modifying agent of PLLA. Firstly, GT Method was used to obtian long side chain NCC-g-PLA (NP) to introduce chain entanglement in molten state. Secondly, GF method was introduced to obtain NP-g-PLLA (NPL) and NP-g-PDLA (NPD) with many short chains to improve the its dispersion and compatability with PLLA matrix. It has been found that the nucleation effect was enhanced remarkably with the adding of 1% NPL or NPD. What’s more, the storage modulus and loss modulus of the composite melts also increased effectively with 1% NPL or NPD. The NPD/PLA complex's values are all higher than that of NPL/PLA nanocomposites under the same loading condition which can be ascribed to stronger interaction comes from the sterecomplex network of PLLA matrix with PDLA short chains in NPD. Meanwhile, the short relaxation time intensity of PLLA has also been enhanced, and the NPD-1/PLLA sample even occurs a much longer and stronger relaxation peak which can be helpful in PLLA’s melt processing.