To meet the requirement of high-power nanosecond pulse emission, an ultra-wideband combined antenna for high-power microwave is designed. Voltage standing wave ratio (VSWR) and electric field distribution of high-power ultra-wideband combined antenna with point-fed balun and tapered-slot balun are compared. The relationship between characteristic impedance and dimensions of the combined antenna is analyzed. Klopfenstein impedance taper is used to reduce reflection. The size of the magnetic dipole is optimized by adjustable plate to improve the low frequency performance of the antenna, and validated by experiment for VSWR testing. On this basis, high-power microwave experiment is performed. With excitation of the high-power bipolar pulse whose bottom width is 3 ns, peak-to-peak value is 121 kV and center frequency is 329 MHz, the power handling capacity of the antenna is 73 MW, effective potential gain is 1.97.