This paper reports a flexible and transparent ultra broadband absorber with ITO film based on cross roundabout pattern. The core structure of the absorber is a sandwich structure of ITO-PET-ITO, in which the top layer is ITO film designed as a cross and roundabout pattern, the middle layer is a flexible and transparent PET substrate, and the bottom layer is covered with ITO film. The simulation results show that the proposed absorber has good absorptive performance, and the bandwidth with absorptive efficiency larger than 99% is 2.2 GHz (from 30.5 GHz to 32.7 GHz); The bandwidth with absorptive efficiency more than 95% is 7.4 GHz (from 28.1 GHz to 35.5 GHz); The bandwidth with absorptive efficiency over 90% is 16.6 GHz (from 21.6 GHz to 38.2 GHz). The bandwidth with absorptive efficiency over 90% covers part of K-band and part of Ka-band and the relative bandwidth is 56%. Under the condition of oblique incidence from 0° to 45°, the absorptive performance of the absorber is relatively stable, which can reach more than 90%.