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Fatigue crack propagation experiment of AZ31 magnesium alloy in different direction were conducted accompanied by acoustic emission monitoring, and the results presented similarities with the conventional results. Acoustic emission hit counts has a liner relationship with the stress intensity factor range during the stable cracking stage, and the turning point of dC/dN-ΔK curves had error of 2.86%(along the rolling direction)and 3.00% (vertical to the rolling direction) with that of da/dN-ΔK. The crack along the rolling direction propagated slower than another direction, and the reason could be listed as follows: there was obvious quasi-cleavage fracture and more twins when the crack propagated vertical to the rolling direction, which could stop cracking at some extent. So the crack resistance of rolling direction below another direction. and acoustic emission technique was a practical method to study the fracture behavior.