Aiming at the issues that current ultra-wideband (UWB) multiple-input multiple-output (MIMO) antennas are prone to signal interference across multiple frequency bands and suffer from poor isolation between ports, a compact high-isolation ultra-wideband four-port MIMO slot antenna with dual-notched characteristics is proposed. The antenna has a dimension of 65 mm×65 mm×0.8 mm. Employing coplanar waveguide (CPW) feeding and integrated with a cross-shaped isolation structure to enhance the isolation between ports, this antenna generates notches in the 3.25~3.85 GHz and 4.32~5.69 GHz frequency bands by etching two C-shaped slots on the radiating patch. These notches can effectively suppress interference signals from the WiMAX (3.3~3.7 GHz) and WLAN (5.15~5.825 GHz) frequency bands. In-depth analyses were carried out on various performance parameters of the antenna, including peak gain, envelope correlation coefficient (ECC), diversity gain (DG), and total active reflection coefficient (TARC). Experimental measurements show that the proposed MIMO antenna operates within the frequency band of 2.48~11.2 GHz, with an isolation of over 20 dB, an ECC of less than 0.07, and a DG of more than 9.97, demonstrating excellent diversity performance. Both simulation and measurement results indicate that the antenna exhibits superior performance in signal transmission and anti-interference capability, with minimal interference between ports. It holds promising application prospects in ultra-wideband MIMO communication systems, particularly in the WiMAX and WLAN notched frequency bands, and can meet the requirements of wireless communication systems.