This work aims to improve surface hardness and wear resistance of 20CrMnTi steel. Composite carbon-niobiumizing coatings were prepared on 20CrMnTi steel surface in powder packing method. The niobiumizing agent was composed of Nb powder, La2O3, Al2O3 and NH4Cl. Treating temperature was 950 ℃ and holding time was 5 h. Microhardness, thickness, microstructure, phase composition and friction coefficient of the carbon-niobiumizing coatings with different content of La2O3 (0%, 0.5%, 1%, 2%) were characterized with OM, SEM, microhardness tester, EDS, XRD and fretting tribotester. Main phase of the prepared coatings with different content of La2O3 was NbC. The thickness and microhardness of carbon-niobiumizing coatings was 23~28 mm and 2250~2950HV0.5, respectively. With the increase of La2O3 content, phase composition of the carbon-niobiumizing coating was similar, both microhardness and grain size of carbon-niobiumizing coatings first increased and then decreased, while the thickness decreased gradually. With the increase of La2O3 content, friction coefficient of carbon-niobiumizing coatings first increased and then decreased. The friction coefficient was the lowest when the La2O3 content was 0.5wt%. In summary, the optimum content of La2O3 in powder-packed composite niobiumizing agent is 0.5wt%. Addition of 0.5wt%La2O3 can refine grains size of carbon-niobiumizing layer, and improve hardness and density of composite carbon-niobiumizing coatings on 20CrMnTi surface.