Abstract: Polydopamine (PDA) and octadecyl isocyanate were selected to functionalize barium titanate nanowires (BTW) and boron nitride nanosheets (BNNSs) respectively, and construct D@BTW-fBNNSs particles. The influences of D@BTW-fBNNSs on dielectric property, breakdown strength and thermal conductivity of poly (m-phenyleneisophthalamide) (PMIA) dielectric were investigated. The results show that, with increasing content of D@BTW-fBNNSs, the dielectric constant of PMIA dielectric significantly increases. The dielectric constant of PMIA composite with 15wt%D@BTW-fBNNSs displays 75% improvement at 10³ Hz compared with PMIA matrix, and the dielectric loss of corresponding PMIA composite maintains at relatively low value. Furthermore, the dielectric properties of D@BTW-fBNNSs/PMIA dielectric are stable under high temperature (>150℃), which can meet the requirement in high temperature environment. Additionally, the thermal conductivity of PMIA dielectric is obviously improved with increased content of D@BTW-fBNNSs. The thermal conductivity of PMIA dielectric with 15wt% D@BTW-fBNNSs is 1.5 times higher than that of PMIA matrix. This research will provide new method and idea for the design of high-temperature polymer dielectric with enhanced dielectric constant and low thermal effect.