Abstract: Focusing on CoCrNi medium-entropy alloy (MEA) and addressing challenges in fabricating and regulating the performance of its ultra-thin strips, this study employed the accumulative roll bonding (ARB) process to overcome conventional rolling limits, successfully producing ultra-thin strips with thicknesses of 0.1-0.27 mm. It was found that with decreasing thickness, grains elongated significantly along the rolling direction, accompanied by synchronous increases in dislocation density and substructure fraction, leading to enhanced strength but reduced plasticity. Specifically, the 0.1 mm strip exhibited a tensile strength of 1 295 MPa and an elongation of merely 2.5%. To optimize comprehensive performance, 750 ℃ annealing treament was further conducted:short-time annealing (5-15 min) is dominated by recrystallization as the primary mechanism, resulting in balanced properties with a tensile strength of approximately 950 MPa and an elongation rate of about 35%. Prolonged holding time to 30 min enhanced internal recovery, increasing the fraction of subgrains and deformed grains to 48.6%; although grain coarsening slightly raised strength to 1 001 MPa, plasticity significantly decreased to 22.2%. This study revealed the correlation between microstructural evolution and mechanical properties of CoCrNi MEA ultra-thin strips, providing important theoretical basis and technical support for their application as ultra-thin metallic materials in high-performance micro/nano devices.