In wireless communication, controlling electromagnetic wave propagation and polarization direction is crucial for signal detection and reception. This study introduces a liquid metal-based electromagnetic metasurface for polarization conversion in the X (8-12 GHz) and Ku (12-18 GHz) bands. It offers benefits like ultra-wideband performance, high polarization conversion ratio, compactness, durability against mechanical fatigue, flexibility, and affordability. The metasurface consists of a periodic arrangement with a top step-shaped liquid metal structure, a middle dielectric layer, and a bottom copper foil, capable of ultra-wideband cross-polarization conversion or wideband circular polarization conversion from 7.595 GHz to 17.712 GHz. With a 1.6 mm wide step-shaped liquid metal structure, it achieves over 90% polarization conversion ratio across 7.595-17.712 GHz with a 79.9% relative bandwidth, enabling co-polarization to cross-polarization conversion. At a 0.3mm structure width, it converts linear to circular polarization between 10.864-12.288 GHz with a 12.30% relative bandwidth. Additionally, in the 7.328-7.592 GHz band with a 3.54% relative bandwidth, it maintains over 90% polarization conversion ratio, facilitating co-to cross-polarization conversion. Experimental sample tests reveal a 4.20% relative error between experimental and simulated results, indicating strong theoretical and experimental correlation, thus confirming the metasurface's versatility and effectiveness.