Abstract: Polypropylene (PP) fibers surface was modified with acrylic acid by chemical grafting method. The effects of modified PP fibers on plastic shrinkage cracking, mechanical properties and bubbles structure of foamed cement were studied. The results show that modified PP fibers can improve bubbles structure, reduce plastic shrinkage cracking and refine plastic shrinkage cracks of the foamed cement, and it can increase flexural strength, compressive strength and flexural toughness. When the mass ratio of modified PP fibers to cement is 0.7%, the bubbles structure of foamed cement is improved significantly, and the plastic shrinkage cracking value decreases by 85.4%, while plastic shrinkage cracks whose width is less than 1 mm is as high as 73.1%. In the meantime, the flexural strength and compressive strength increase by 48.8% and 30.3%, respectively, and flexural toughness increase significantly. The surface groups of PP fibers before and after modification and the fracture surface micro-morphology and bubbles structure of foamed cement were observed by FTIR spectrometer, SEM and optical microscope. The action mechanisms of modified PP fibers were discussed.