A CPW-fed planar wide-slot antenna was designed. The Koch fractal technology was used to broaden the bandwidth of the antenna, and the HFSS software was used to optimize the size and position of the CPW feeder and the rectangular matching stub. The return loss, the pattern and the gain of this wide slot antenna was measured. The measured result showed that the bandwidth of the antenna reached 14~5.8 GHz, and the in-band gain fluctuation was less than 3dB. The research of this antenna system had strong expansibility and application prospects in power detection, 5G communication, radar system, etc.