Abstract: For the purpose of investigating the hydrolysis performance of bifunctional vinylsulfone reactive dyes in cold pad-bath dyeing, the high performance liquid chromatography was applied to analyze the process of hydrolysis of C.I.Reactive Black 5 qualitatively and quantitatively at low-temperature. The results showed that the rate of elimination reaction and hydrolysis reaction increases with the increase of pH value. In the alkaline solution, both of the reactins are of pseudo first-order. When the temperature is 30℃ and pH=9,the rate of hydrolysis of C.I. Reactive Black 5 is 3.5×10-5/min-1, and the rate of hydrolysis of C.I.Reactive Black 5 at pH=10,pH=11,and pH=12 is about 3 times,27 times, and 233 times higher than that of C. I. Reactive Black 5 at pH=9, respectively. The result of the present work implied that C. I. Reactive Black 5 has a relatively stable performance.