Integrated boost-flyback step-up converter (IBFC) has the ability of high voltage gain in the case of small duty cycle, thereby avoiding high power loss of circuit under the limit duty ratio which compared with traditional boost circuit. Integrated coupled-inductor boost-flyback converter (ICBFC) is presented, which utilized the coupled inductor instead of the power inductor of the IBFC. This paper studies the quantitative relationship between parasitic parameter, boost characteristics and efficiency of ICBFC, which meanwhile explores the best design parameters in specific cases. Comparing two kinds of topologies, the advantage over IBFC of the ICBFC reduces current stresses of diode and voltage ripple of capacitors at the same time by introducing the actual parasitic parameters under the condition of same voltage gain. Experimental results are given for hardware verification. The theoretical analysis and simulation agrees well with experimental results.