The invention relates to a method for preparing a boron doping conducting diamond film which relates to the film technique field. The method includes steps as follows: dissolving trimethyl borate into acet with pre-set B/C ratio, placing the dissolved trimethyl borate in a bubbler bottle with 0 DEG C all the time for controlling flow of carbon source and boric source. Part hydrogen flow is used as carrier gas for taking out of liquid steam by using bubble method. Ploblem that trimethyl borate doping boron decomposes boric acid leading to block flowmeter, needle valve and pipe will not occurred. The prepared thin-film has lower resistance ratio (10<-3> omega.cm), the diamond component have the trump card and good quality. The boron doping preparing process is safe and no toxicity, and has no pollution of boric source to atmosphere.