Abstract: The nano crystalline cellulose (NCC) was prepared through a sulfuric acid hydrolysis process, Then NCC was chemically modified with N, N-carbonyldiimidazole (CDI) and 2-Methyl-2-propen-1-ol (MPO) to obtain propenyl carbonate NCC (PCNCC). 4,4′-diamino diphenyl methane bismaleimide (MBMI), 3,3′-diallyl bisphenol A (BBA) and bisphenol-A diallyl ether (BBE) were used to synthesize MBMI-BBA-BBE (MBAE) matrix. The modification results were characterized by FTIR, XRD, TEM and iodine value method. When the replacement rate of PCNCC is 16.4%, the modified PCNCC preserve their type and high degree of crystallization, The PCNCC stably suspend in BBE; PCNCC with too low or too high replacement rate are not suitable for fillers in PCNCC/MBAE composites. The PCNCC/MBAE composites were prepared by doing PCNCC in an MBAE matrix by in-situ polymerization. The effects of modified PCNCC mass fraction on the mechanic properties, dielectric properties and thermal properties of PCNCC/MBAE composites were investigated. A strong interaction is observed between the PCNCC and MBAE, When the mass fraction of PCNCC is 0.2 wt%, the flexural strength and modulus of PCNCC/MBAE composite are 148.1 MPa and 6 GPa, increased by 50.5% and 82.9% than that of MBAE matrix. The impact strength of PCNCC/MBAE composite is 13.9 kJ/m², increased by 54.8% than that of MBAE matrix, respectively. The glass transition temperature T_g value from 240.4℃ of the pure MBAE to 257.8℃. The dielectric constant of PCNCC/MBAE composite increases and the dielectric loss reaches the lowest value. The improvement of mechanical properties and thermal stability of PCNCC/MBAE composites provides theoretical data for the expansion of nano cystalline cellulose and bismaleimide resin applications.