The highly thermosensitive mutant Z114 can be easily released intracellular protein to extracellular environment， when the cells form the Z114 are incubated both in the low-osmolarity water and at the non-permissive temperature （usually 37 ℃）， the fermentation condition is the pH natural， the fermentation temperature 28 ℃， the yacon extract 180.0 g/L， soybean cake hydrolysate 25.0 g/L， ammonium sulfate 15.0 g/L， the crude protein content was 59.1% attained at 45 h of the fermentation. The attained cell from the mutant Z114 were treated at 37 ℃ overnight， there was 61% intracellular protein that was released from the mutant cell. The content of the protein produced by the mutant Z114 was kept high level， the essential amino acids and other nutrients were rich. This means that the yacon extract could be used as the medium for growth of the highly thermosensitive to produce to protein.