Abstract: This paper presents a predistorter without DC bias for Kuband space TWT. It is composed of a 3dB hybrid coupler, a pair of GaAs antiparallel Schottky diodes and load resistance，which generates the distorted signal. It is adjustable by changing the length of microstrip line and the load resistance. Besides, the predistortion circuit shows the perfect input/output matching characteristics which makes it small size and simple configuration.The tested results show that, in the bandwidth range of 500MHz, about 7dB gain expansion and 45° phase shift can be compensated for the TWTA, and the improvement of about 6dB the thirdorder intermodulation (IM3) at TWTA dual saturated Input Power Back Off(IPBO) of only3dB can be reached with the predistorter.