ZL205A alloy samples were obtained by melting ZL205A alloy and different percentage of yttrium. The effects of yttrium contents to as-cast microstructure and solidification process of ZL205A alloy were studied by optical microscope （OM）, scanning electron microscope （SEM） and thermal analysis. Etc. The results showed that the element cause a depression of the eutectic arrest, reduction of freezing range and also result in refined and modified to as-cast microstructure and θ（Al2Cu） phases, respectively. When yttrium content was 0.05 wt.%, the mechanical properties of alloy were better than primary alloy, but with further increasing of the yttrium content, the mechanical properties deteriorated. However, the addition of yttrium of making the microstructure fine is 0.3%. The mechanical properties were better again.