Abstract: This paper briefly introduces the design of a W-band extended interaction klystron (EIK), and gives the test results. The high frequency extended interaction circuit consisted of five 5-gap buncher cavities and one 11-gap output cavity which can obtain wider bandwidth. This ladder-type multi-gap cavity circuit is easy to fabricate and supports greater energy margins. The π-mode is selected as the operating mode of the 5-gap (or 11-gap) cavities. By now, with an electron beam of 17 kV and 0.78 A, the EIK has achieved a peak output power of 2 kW, bandwidth of 500 MHz, gain of 40 dB, and duty cycle of 5%.