In this article, we utilized a facile approach for growth of carbon nanotubes onto the surface of carbon fibers by microwave plasma‐enhanced chemical vapor deposition to improve the interfacial properties of composites. By adjusting the deposition time, the length and density of carbon nanotubes could be controlled, and the results of Brunauer–Emmett–Teller testing indicated that the specific surface area was increased with the deposition time prolonged, which improve the contact area between fiber and resin matrix. The interfacial shear strength of the composites increased significantly with increasing in deposition time. When the deposited time reached 15 min, the interfacial shear strength of carbon fiber/epoxy composites increased 153%, reaching to 129.92 Mpa. On the basis of investigation for the relationship between the interfacial properties and the micro‐structures of composites, we found that the propagation path of transverse cracks on interface increased with the increasing of interfacial properties. POLYM. COMPOS., 39:E1262–E1268, 2018. © 2018 Society of Plastics Engineers