The recently proposed current-fed quasi-Z-source inverter (QZSI)  can buck/boost voltage and provide bidirectional power flow . A crucial criterion for the size of three phase PWM converters is the cooling of the power semiconductors and thus determination of power dissipation at certain operating points. A complete analytical calculation of the power loss for current-fed QZSI is presented. Inverter bridge loss, inductor loss and diode loss are included in this part. In order to bring the prototype into real application in hybrid electrical vehicle , the inverter efficiency is measured according to the motor P-V curve. In addition, this paper discusses two factors that influence the efficiency: operation point and switching pattern. Higher input voltage and higher modulation index could lead to higher efficiency. Also an improved switching pattern is proposed to reduce the inductor current ripple without increasing the switching loss, which could lower the inductor value for a given current ripple requirement, thus reduces the conduction loss. Finally the experimental results are given to verify the power loss calculation algorithm and the validity of the method proposed to improve the efficiency.