One of the key issues to deeply understand the intrinsic mechanism of Portevin-Le Chatelier (PLC) phenomenon is to analyze the spatial distribution and the evolution of the deformation in PLC bands, associated with serrated yielding. In this work, an investigation was carried out with 5456 aluminium magnesium alloy sheet specimens of different thicknesses at room temperature by using three dimensional digital image correlation (3D-DIC) method, which focused itself on the deformation analysis within serrated yielding under different loading procedures. After statistically analyzing loading curves, it is found that the average amplitude and average period increase with increasing strain. Moreover, there is a positive correlation between the average period and the thickness of specimen, while the average amplitude and the thickness of specimen are independent to some degree. In addition, the experimental result also indicates that the width of the PLC band increases with increasing thickness of the specimen. However, the spatial analysis in PLC bands proves that the angle between the PLC band and the tensile direction is about 60°, which is irrelevant to the specimen thickness and the serration amplitude. Furthermore, it is also found that PLC bands of out-of-plane displacement coincide with bands of strain in the tensile direction by temporal analysis. Most importantly, the experimental result shows that the serration amplitude is proportional to the maximum strain in PLC band when PLC band occurs.