The Present invention is drawn to processes f or biologically controlling T7 expression system in Recombinant Escherichia coli strain BL21(BAD) by using L-arabinose to active T7 promoter. The strain BL21(BAD) are useful to produce a variety of het erologous proteins. Also disclosed is abiologically large scale operations of the strain BL21(BAD), it is convenient to carry out the culture in a fermen tation tank with two-stages carbon source and sta ge input system.
