To systematically study the relationship between foreign protein expression and relative cell viability caused by different modules,we investigated the recombinant human hIFNβ-HSA fusion protein in Pichia pastoris KM71/IH.The results showed that;(1) There were positive correlations between the expression of foreign protein and relative cell viability;(2) Cells on midanaphase of logarithmic growth were much more suitable for foreign protein expression,because of high cell viability;(3 ) Environmental factors of induction period directly influenced the relative cell viability.The methanol concentration,induction pH and temperature were optimized to promote expression of proteins.The optimal induction conditions to express hIFNβ-HAS is;21～24 h yeast cells,2%(V/V) methanol,pH 6.0,25℃.The relative cell viability could remain more than 98%under those conditions,and the yield of hIFNβ-HSA reached 45.6 mg/L,which was 62.3%higher than that of the control.