The CrCuFeMnNi high entropy alloy (HEA) powder was synthesized by mechanical alloying. The effects of milling time and subsequent annealing on the structure evolution, thermostability and magnetic property were investigated. After 50 h of milling, the CrCuFeMnNi HEA powder consisted of a major FCC phase and a small amount of BCC phase. The crystallite size and strain lattice of 50 h-ball-milled CrCuFeMnNi HEA powder were 12 nm and 1.02%, respectively. The powder exhibited refined morphology and excellent chemical homogeneity. The supersaturated solid solution structure of the as-milled HEA powder transformed into FCC1, FCC2, a small amount of BCC and ρ phase in annealed state. Most of the BCC phase decomposed into FCC (mainly FCC2 phase) and ρ phases, and the dynamic phase transition was almost in equilibrium at 900 ℃. The saturated magnetization and coercivity force of the 50 h-ball-milled CrCuFeMnNi HEA powder were respectively 16.1 emu/g and 56.2 Oe.