A new type of S-band multibeam klystron has been developed at the Institute of Electronics, Chinese Academy of Sciences, China. The main methods for obtaining wide bandwidth include a multibeam electron gun with 18 beams, a periodic permanent magnet focusing system, a wide-band bunching system and filter-load double-gap coupling-cavity output circuit. The design methods and experimental results are given in this paper. The test results show that this device has a peak power of 120-160 kW, a bandwidth of 10%, a gain of 41 dB, a beam voltage of 16 kV, a weight of 45 kg and a length of 700 mm.