Concentrating solar thermal systems (CSP) have recently introduced as solar technologies that used for electrical power generation by heating a working fluid to high operating temperature range (≥300 oC) and combining it with a thermodynamic power cycle. This study is carried out to develop a Mathcad mathematical model for simulation and analyzing the performance of a pre-design integrated solar combined cycle power plant (ISCC). The system performance analysis results show that the ISCC operation mode raises the plant capacity from 503 MW to 555.23 MW in summer months. The annual solar share of electrical energy is approximately 85.77 GWh and the annual reduction in CO2 emission are approximately 51670.8 tons.