Using sodium alginate as embedding agent, glutaraldehyde as crosslinking agent and calcium chloride as filling agent immobilize the genetic engineering bacteria with tryptophan synthetase. The effect of the concentration of sodium alginate, glutaraldehyde and calcium chloride and the bacteria load were investigated. And then these factors were optimized by response surface method, in order to determine the optimal immobilized conditions. After that, using the best immobilized bacteria synthesize L-tryptophan and making sure the optimum substrate concentration and the amount of immobilized bacteria. The best preparation conditions for the immobilized bacteria are 28.92 g/l sodium alginate, 0.95% glutaraldehyde, 19.82 g/l calcium chloride and 25 g/l bacteria load. The best synthesis conditions of tryptophan are 1% L-serine and 8 g immobilized bacteria. The average conversion rate from substrate is 28.16%. The immobilized bacteria can be used continuously for 15 times.