A new steady state modeling of unified power flow controller (UPFC) is proposed in this paper. Using this model, factors that affect the objective function of electricity market as a result of UPFC installation in power grid has been decomposed into four components, including line series impedance increase, shunt reactive power compensation, inphase component of series voltage and quadrature component of series voltage. A UPFC has been placed in different points of a test system and impact of each component on objective function of electricity market has been measured by simulation and compared with results from analytical method. Both active and reactive power spot prices are calculated and their relation with settings of UPFC series part has been studied. Also, numerical results shows that the necessary cost to improve security of electricity market decreases by UPFC installation.