The invention specifically relates to a method for on-line and in-situ preparation of silica whiskers in the interior of a carbon-ceramic composite material. The invention mainly solves the problems of needing of a high environmental temperature, needing of a heating process, large reaction gas flow rate and inapplicability to reaction in the interior of a ceramic based composite material for a conventional method of preparing nanometer silicon dioxide. The method comprises the following steps: 1) placing a silicon carbide ceramic-based composite material into a chemical vapor deposition furnace, wherein a temperature of the interior of the furnace is 900 to 1100 DEG C; 2) introducing mixed gas of precursor gas prepared from a silicon carbide ceramic matrix and air into the deposition furnace, and carrying out a reaction; and 3) allowing the silica whiskers to be formed in the interior of the ceramic based composite material on line and in situ. The method provided by the invention needs a low environmental temperature, has small reaction gas flow rate, and can effectively reduce cost.