In this paper, the mathematical modeling of Cuk converter operating in continuous conduction mode (CCM), is done by using the signal flow graph (SFG) method and Meyson gain formula. By using the obtained model, the output voltage to input voltage transfer function and also the output control transfer function are extracted. Moreover, the effects of equivalent series resistors (ESRs) on stability and frequency response of Cuk converter are investigated in four different states, the roots location and bode diagram of each state have been studied by using related obtained transfer function. The simulation results are presented to verify the SFG performance and also the effects of the inductors and capacitor resistances on stability and frequency response.