Textures, significantly affecting the anisotropy and the related key properties, are often used as variables for industrial control. However, compared with many technological studies, the texture-related mechanisms during friction stir processing (FSP) are insufficient, including P orientation associated with precipitation. These knowledges are useful for understanding the nature of materials and achieving control of properties. In this experiment, FSP was used to obtain a nearly defect-free processing zone in Al-Mg-Sc alloy, and the changes in orientation of stirring zone were discussed to determine main texture types and the causes of their formation. In addition, after FSP, the P orientation decreased monotonically as the distance from the top increased, regardless of how the main texture changed. The orientation of crystallographic coordinates of all P oriented grains in the sample coordinate system indicated that P oriented grains came from two parts, one was the growth of P cores mainly formed by the shoulder, the other was the transformation of non-P oriented grains due to the dominant direction of 45° ~ 52°〈111〉. Finally, the effect of nanoscale Al3Sc precipitates on texture, especially P orientation, was analyzed. As the distance from the top increased, the density of Al3Sc precipitates on grain boundaries increased, which limited the preferred growth required by the texture including P orientation, and the texture tended to be random.