A highly active nitrile hydratase/amidase system was found in Gordonia sihwensis CGMCC 4.2184, which was capable of converting 2-hydroxy-4-methylthiobutanenitrile (HMTBN) to 2-hydroxy-4-methylthiobutanamide (HMTBAm) by nitrile hydratase and then 2-hydroxy-4-methylthiobutanoic acid (HMTBA, methionine hydroxy analogue) followed by amidase in in-situ cascade manner. The effects of substrate concentration, cell concentration, temperature, pH and reaction time on nitrile hydratase and amidase activity were investigated. The thermal stability and pH stability of nitrile hydratase and amidase were determined. The results showed that the optimal reaction conditions were: 50mmol/L HMTBN, 3g/L dry weight cells, 30℃, pH8.0, 30min. Under the optimal reaction conditions, the cells could be used in 23 batches, and the cumulative amount of HMTBA reached 164g/L in 44h, with a yield of 95%.