In this work, a precipitation-hardened HEA was developed. The strengthening originates from high-density L12 particles, whose size ranges from 5 to 20 nm, depending on thermal treatment conditions. The average size, density, and volume fraction of the precipitate were analyzed quantitatively. The deformation microstructure of alloys with different mechanical properties were also analyzed and compared. It was found that planar slip band is the predominate structure at the early stages of deformation, but the activation of the second slip direction is observed at strains as low as 0.02. The interaction between dislocation and precipitates changes with precipitate size. At small precipitates sizes, dislocations shear and move through the particles. However, looping was observed in alloys with larger precipitate sizes. The effect of such transition on the deformation microstructure and mechanical properties is probed, and the conditions for optimized mechanical property is discussed.