For making a complex synthetic gene network function as designed, the parameters in the network have to be extensively tuned. In this study, a simple and general approach to rapidly tune gene networks in Escherichia coli was developed, which uses the hypermutable simple sequence repeats embedded in the spacer region between the ribosome binding site and the initiation codon. It was found that the change of sequence length and compositions of the repeated base pairs in 5'UTR contributes together to the changeable expression levels of the target gene. The mechanism of this phenomenon is that the transcriptional process makes greater impact on the expression level when compared to the translational process, which is utilized to successfully predict sample gene expression levels over a 50-fold range. The utility of the approach to regulate heterologous ecaA and pepc gene expression in the engineered E. coli for improving succinic acid yield and production has also been demonstrated. When the expression level of ecaA gene was 3.53-fold of the control and the expression level of pepc gene was 1.06-fold of the control, the highest yield of succinic acid and productivity were achieved, which was 0.87 g g(-1) and 2.01 g L-1 h(-1), respectively.