This paper presents a novel approach to depict Flexible AC Transmission Systems (FACTS) devices effects in power system using multi-objective optimization function. The FACTS devices can play very important roles in power system such as improve power system security, reduce generation cost, decrease transmission loss and improve the voltage stability index. Two more common FACTS devices are the Thyristor Controlled Series Capacitor (TCSC) and Static VAR Compensator (SVC) which can smoothly and rapidly change their apparent reactance and injection power respectively according to the system requirements. Determining the FACTS devices parameters in power system is too complicate and has a lot of local optima in its search space. In order to overcome above problems a new method, based on SFLA algorithm combined with a new mutation is proposed to increase the efficiency of the SFLA algorithm. Since the proposed problem is a multi-objective problem it is usual to obtain a set of solution instead one solution therefore Pareto method that uses concept of non-dominate solutions is applied to find best compromise solutions. An external repository is considered for saving all non-dominated solution, and also they are sorted by fuzzy set rule to obtain best solutions. For more validation the simulation results are compared with those in other literatures.