The invention discloses a method for preparation of surface active onion-like carbon nanospheres based on vapor deposition. The method includes: taking liquid small organic molecule alkane n-dodecane as the carbon source, carrying out chemical vapor deposition reaction at a high temperature of 650-700DEG C in an inert carrier gas environment with the existence of a ferrocene catalyst to directly prepare the high surface activity onion-like carbon nanospheres composed of onion-like graphitized shell coated ferroferric oxide nanoparticles. The onion-like carbon nanosphere product prepared by the method provided by the invention has good surface activity, thermal stability and wide practicability, and can be applied to adsorption materials, energy storage materials, catalytic materials, medical materials, and other fields.