Abstract: Basic non-isolated buck-boost circuit exists the problem of short-circuit ring caused by the diode-s reverse recovery. A buck-boost DC/DC converter based on Z-sourse was designed. The presence of short-circuit ring was avoided from the circuit structure. The step response of initial state of the Z-network and the converter were discussed. The pre-charge circuits was also designed. The voltage and current spikes when the converter started were also eliminated. The three operation modes and operation theory of the converter was analysed when it worked in the situation of inductor current continuous mode(CCM). The operation modes of the boost and buck mode were simplified according to the principles of optimal efficiency, thereby the control strategy was also optimized. A method was presented to ensure the converter worked in CCM through choosing the reasonable inductor ripple factor. The design rules of the components was also given. Smulation and experimental results coincide with the theoretical analysis.