It is well known that the reaction between UF_6 and SiH_4 cannot take place below 140℃. Recently we found in our experiments that this reaction can proceed at a high speed by catalyzing with HBr at room temperature, producing UF_4 and other products. In this note the HBr-catalyzed reaction of UF_6+SiH_4 and the kinetic mechanism of the catalyzed reaction are investigated. 1 Experimental UF_6 gas, produced by the 404th Factory of Nuclear Industry Corporation, was vacuum-distilled and cold-trapped several times at dry ice temperature (-78℃) in a metal vacu-