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The resistance values of two layers directly coupled differential-common emitter voltage series negative feedback amplifying circuit are adaptively optimized by particle swarm optimization. In the method, the voltage gain, common-mode rejection ratio and the square root of the input resistance are multiplied, and the ratio between the product and the output resistance is used as the fitness function. The results indicate that the fitness function value will decrease under the constraint condition that alternating current index is limited. After increasing voltage gain and decreasing the output resistance are restricted, to derive the maximal fitness function value under the given condition, the voltage gain is as small as possible and the output resistance is as large as possible. Simulation results of the parameters with EWB software can meet the requirements of linear amplification. The results also indicate that the optimal parameters of circuit can be found by adjusting the fitness function. [ABSTRACT FROM AUTHOR]