With the extraordinary development of electronic technology, complexity of circuit system increases sharply. More and more electric circuits are composed of digital and analog signal simultaneously, resulting in greater difficulty in circuit testing. Theory of Discrete Event System(DES) and relevant researches provide uniform, efficient and systematic methods for testing these mixed-signal circuits. In view of the circuit testing based on DES theory, how to find out the minimal test set of circuits is important part to shorten complicated work. Considering advantageous characteristics of the minimal test set, a novel approach involving with minimizing mixed-signal circuit testing-set algorithm is put forward, which is in light of Discrete Particle Swarm Optimization(DPSO) and can finally realize optimization. By virtue of "velocity-position" model referred to competition and cooperation among particles of swarm, an optimum solution is searched in result space. Experimental results testify high efficiency and feasibility of this proposed approach, which is superior to other optimization algorithms.