Abstract: To study the effect of surface modification,we modified three kinds of plant fibers (bamboo fiber, fir fiber, jute fiber) in situ with calcium carbonate. The pressing technology was used to prepare plant fibers reinforced polypropylene composites. The surface morphology, surface roughness, statics contact angle (SCA) and tensile property of plant fibers and their composites were examined by scanning electron microscopy (SEM), atomic force microscope and optical contact angle measuring device. The results indicated that CaCO3 in situ modification had a marked effect on the surface properties of single plant fibers, which not only improved the tensile properties of single plant fibers, but also developed the interface properties of plant fiber-reinforced thermoplastic polymer and enhanced the interface strength of the composite. After the treatment of in situ deposition, CaCO3 particles were successfully deposited to all three kinds of plant fibers, and the CaCO3 loading of fir fiber was the highest, reaching 16.08%, and that of bamboo fiber was the lowest, 6.96%. The Rq value of bamboo fibers was reduced by 32.95%, SCA was increased by 1.85%, and Rq value and SCA of fir fibers were increased by 42.51% and 3.12%, respectively, while the Rq value of jute fibers was increased by 62.77% and SCA was reduced by 0.4%. The tensile properties of all three kinds of single modified plant fiber were improved, and that of the single modified bamboo fibers were the best, reaching 1 134.83 MPa and 37.25 GPa, respectively. SEM images of fracture morphology showed that the interfacial adhesion between modified plant fiber and PP was stronger, forming a dense interfacial bonding layer. Fiber pullout decreased at the junction of composites, and the damage was mostly in form of fiber breakage. CaCO3 in situ modification developed the interface properties and thus improved the tensile properties of modified plant fiber-reinforced PP composites. In addition, the trend of change of MOE was consistent with that of loading of CaCO3, and the MOE of modified fir fiber-PP composites was maximum, reaching 2.28 GPa, while the tensile strength of modified bamboo fiber-PP composites was the highest, achieving 54.04 MPa.