NOVELTY - Preparing hydrazone compound involves taking para-chlorobenzene hydrochloride and dissolving in deionized water, under protection of inert gas, extracting polychlorinated biphenyl to form para-chlorobenzene hydrazine hydrochloric acid salt aqueous solution, weighing aldehyde compound and mixing with deionized water to form aldehyde compound aqueous solution, mixing solutions with water, controlling temperature and adding speed of solutions, centrifuging, dissolving solid crude product in organic solvent and water, and crystallizing.    USE - For the preparation of hydrazone compound (claimed) used as organic chemical intermediate for forming inert gas-containing heterocyclic compound; and as intermediate in the preparation of medicine and pesticides.    ADVANTAGE - The preparation method avoids formation of hydrazine impurity, allows recycling of excess of alcohol type compounds, is economical and environment-friendly.    DETAILED DESCRIPTION - Preparing a hydrazone compound involves under the protection of inert (N2) gas reacting aldehyde compound with para-chlorobenzene hydrazine hydrochloride, where the reaction formula is as follows: para-ClC6H4N2H3-HCl+RCOCHO to form para-ClC6H4NHNCH-COR+ HCl+H2O, where the method includes taking para-chlorobenzene hydrochloride and dissolving in deionized water, under the protection of inert gas, extracting polychlorinated biphenyl to form para-chlorobenzene hydrazine hydrochloric acid salt aqueous solution, weighing aldehyde compound and mixing with deionized water to form aldehyde compound aqueous solution at a concentration of 0.5/l, taking para-chlorobenzene hydrazine hydrochloric acid salt aqueous solution, and the aldehyde compound aqueous solution, mixing with water in a reactor, controlling the reaction temperature in the reactor at 20-30 degrees C, where the reaction pH value is 3-6, controlling the adding speed of para-chlorobenzene hydrazine hydrochloric acid salt aqueous solution at 0.1-0.2 mol/minutes, controlling the adding amount of aldehyde compound aqueous solution at 0.15-0.25 mol/minutes in the reaction process, stirring and controlling the stirring speed at 80-100 r/minutes, centrifuging the reaction material to form solid crude product and mother liquid, dissolving solid crude product in organic solvent and water, heating, cooling and crystallizing the product to form the final product.    R=H or alkyl (preferably methyl, ethyl, propyl or butyl).