Effects of the polypropylene fibers, modified by alkali treatment and VAE emulsion coating treatment, on mechanical properties and softening coefficient of thermal insulation materials were investigated. The results show that compared with the control samples, flexural strength and compressive strength of samples with polypropylene fibers content of 1.0% （by mass） are enhanced by 93.75% and 7.30% respectively. Interfacial bonding between polypropylene fibers and matrix is improved after the fibers were modified by alkali and coating treatments. Compared with unmodified fibers reinforced samples, flexural strength and compressive strength of samples, with polypropylene fibers modified by alkali treatment, are increased by 14.52% and 4.08% respectively, however, softening coefficient keeps almost the same. The flexural strength, compressive strength and softening coefficient of samples, with the fibers modified by VAE emulsion coating treatment, are increased by 58.06%, 10.20% and 12.50% respectively. Micro morphologies of polypropylene fibers before and after different modifications, and fracture morphologies of the samples observed by SEM can be used to elucidate the mechanisms of modified polypropylene fibers in improving performances of vitrified small ball thermal insulation materials.