PURPOSE: To obtain the subject compd. in high yield while minimizing the formation of a poly-fluorinated product, a high b.p. compd. and tar by bringing 1,1- dichloroethylene and anhydrous HF into contact with each other in the presence of an aluminum fluoride catalyst in a gaseous phase.

CONSTITUTION: 1 mol of 1,1-dichloroethylene and 4-8 mol of anhydrous HF are brought into contact with an aluminum fluoride catalyst in a gaseous phase at temp. of up to 120°C (pref., 55-95°C) to obtain the objective compd. The contact time is pref. 1-30 sec. The above mentioned catalyst is obtained by treating anhydrous AlCl3 or AlBr3 or alumina with a volatile fluorine-containing compd. (e.g. HF). The above mentioned alumina may be impregnated with Ni, Cr or Co compd.