In this paper, the mutation breeding on ,Escherichia coli, producing tryptophanase was studied after low energy N,+, ion beam implantation. Parameters in the N,+, ion beam implantation were firstly determined. It has been indicated that a high mutation rate of ,E.coli, could be obtained by N,+, implantation with 10 keV and 13×10,14, N,+,/cm,2, when glycerin at 15 % concentration used as protector. After continuous mutagenicity a high-yield tryptophanase-producing strain has been screened out and both of its biomass and enzymatic activity are higher than the previous levels respectively. The results of scale-up production show that the biomass could be reach 8.2 g,ww, ·L,-1, and 110 g L-tryptophan could be formed in the volume of 1L enzymatic reaction system. In addition, the characteristics of its stable descend ability and easy operation make it a promising strain for industrialization.