Abstract: In this study, the effects of high-pressure torsion (HPT) processing and subsequent annealing on the microstructure and mechanical properties of the Fe₅₀Mn₃₀Co₁₀Cr₁₀ multi-principal element alloys (MPEAs) are investigated systematically by employing X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) techniques. The results demonstrate that HPT processing significantly refines the grain size, promotes martensitic transformation, and introduces dislocations of high density and shear bands. The annealing temperature exhibits a significant influence on the phase transformation, recrystallization, and evolution behaviors of the precipitation of the present MPEAs. When the annealing temperature is 400 ℃, the martensitic phase dominates, and a small amount of Cr-rich precipitated phases exists. When the annealing temperature is 600 ℃, the martensitic phase still predominates, the content of austenite rises, and the morphology of Cr-rich precipitates has changed. When the annealing temperatures are 700 ℃ and 800 ℃, the degree of recrystallization significantly increases, the austenitic phase becomes the main phase, and the Cr-rich precipitated phases decrease. When the annealing temperature increases to 900 ℃, the alloy is almost entirely austenite, and the Cr-rich precipitates disappear. When the annealing temperature further increases to 1 000 ℃, the martensitic phase reappears, and the grains coarsen obviously. Hardness tests reveal that the HPT treatment leads to a notable increase in the hardness of the observed MPEAs from the center along the radial direction. However, with the increase of the annealing temperature, the machining stress is eliminated, the recrystallization degree improves, the dislocations are annihilated gradually, and the Cr-riched precipitated phase decreases and disappears eventually. Due to the combined action of multiple reasons, the overall hardness of the MPEAs gradually decreases.