In order to study the effect of laser shock processing (LSP) on the high cycle fatigue properties of AZ91D-T6 cast magnesium alloy, the test samples with center hole are shocked with Ndglass laser with the wavelength of 1064 nm and pulse width of 20 ns. Tensile-tensile fatigue test is also carried out on the samples. The surface morphology, surface micro-hardness, microstructures, fatigue fracture characteristics and residual stress are analyzed. The results show that after LSP with power density of 1.5 GW/cm2 and spots of 50% overlap rate, high residual compressive stress is generated on the upper and lower surface of the fatigue samples. The micro-hardness of shocking area increases by about 24% and the grains are refined obviously. Fatigue life of the shocked samples is improved by 33.7% than that of the un-shocked samples. The Fatigue fractures show characteristics of the cleavage fracture, and the cleavage steps and river pattern are mainly observed. The crack propagation path is changed because of the existence of the β-Mg17Al12 phase. The crack initiation time is delayed after LSP, which improves the fatigue life of AZ91D-T6 cast magnesium alloy.