Abstract: By using the HY-1 strain Bacillus Licheniformis to produce the thermostable α-amylase,the changes of every kind of parameters such as:the concentration of dissolved oxygen and pH of fermentation liquid were studied.The results of experiments showed that the use of continuous controlling method broth of pH valve had advantage over the pulsed controlling method of pH valve for the fermentation of thermostable α-amylase.The resulted broth of the former showed higher enzyme activity than the latfer.In the period of producing thermostable α-amylase,the cells could produce the thermostable α-amylase under rether low concentration of dissolved oxygen,butthislowleveloftheconcentrationofdissolvedoxygenshouldbeabove10%(DOvalve).

Key words: Thermostable α-amylase , Bacilluslicheniformis, Concentration ofdissolve doxygen, Continuous controlling, Method