The emphasis of this thesis is to reveal the influence of casting methods, anodizing time, anodizing voltage and pretreatment on the thickness of the oxide layer. Al-Si substrate, which is ENAC 42000 aluminum alloy cast by rheocasting and full-liquid casting is used for the investigation. And the modification is introduced to change the morphology of silicon particles. Three different voltage sets, namely 15V, 20V, 25V and four-time sets, namely 15 minutes, 30 minutes, 45 minutes and 60 minutes and three different pretreatments methods, namely mechanical grinding, chemical treatment and chemical treatment after mechanical grinding are designed for comparison. After anodizing, the thickness of the oxide layer is measured by optical microscope. Besides, the microstructure of the substrates and oxide layer is observed and analyzed by the scanning electron microscope. It has been demonstrated that the increase of anodizing voltage and anodizing time will increase the thickness of the oxide layer. But the influence of increasing voltage on the thickness of oxide layer is more significant than the increase of anodizing time. In this study, comparing the results of oxide layer thickness measurements, it was found that the casting method does not have a significantly influence on the thickness of the oxide layer when samples were anodizing at low voltage with short time. However, with the applied voltage higher than 20 V and anodizing time longer than 30 mins, the thickness of the oxide layer on the full-liquid cast samples is higher than the samples which are cast by rheocasitng method.