With the rapid development of the construction industry and higher requirements on the properties of materials, extensive studies have been made to improve the property of the concrete and cementitious materials. This paper mainly studies the mechanical property, anti-chlorine ion diffusion, anti-chlorine ion diffusion, anti-freezing performance, hydration process, microstructure and rheological property of the concrete and cementitious materials after adding cellulose nanofibers. Results showed that the compressive strength of C40 concrete with 0.15% cellulose nanofibers added was 75.72 MPa at 56 days of age, 23.11% higher than that of the control group. It was also higher than that of concrete with 0.20% cellulose nanofibers admixture added. When the content of cellulose nanofibers was 0.15%, the flexural strength reached the maximum value of 6.55 MPa, improving by 24% compared with the control group. Under the circumstances of 150 freeze-thaw cycles, the mass loss rate of C50 concrete with 0.15% CNFs admixture registered at 0.41%, reducing by 0.81% compared with the control group. However, when the cellulose nanofibers increased to 0.20%, the mass loss rate of the concrete reached 0.48%, indicating that adding an appropriate amount of cellulose nanofibers could improve the performance of the concrete. The study provides a strong scientific basis for modifying concrete and cementitious materials.