The measurement of ship model wake field through experiments can provide data support for the optimal design and numerical simulation of the ship. based on the JBC (Japan Bulk Carrier), the longitudinal stern flow field is accurately measured by using time-resolved particle image velocimetry (TRPIV) in a low turbulence return flow wind tunnel. The scale of double deck ship model is 1∶150, and the Reynolds number based on the length between perpendiculars is 2.56×10⁶. The flow normal average velocity field, Reynolds stress and instantaneous vorticity field of stern flow under the design condition are obtained through calculation, and the average velocity field of the spread normal plane is constructed through multiple flow normal average velocity fields. The measurement results show that there is a wide range of low-velocity regions in the stern flow field, and the low-velocity regions shows an obvious "hook" distribution in the flow normal field of view, with obvious characteristics of a large vortex structure, and this vortex structure directly affects the velocity distribution of the wake field. The results of the instantaneous vorticity field show that the vortex structure mainly exists on the upper and lower sides of the propeller boss, and its normal position gradually rises with the outward shift of the field of view, and the large range of vortex structure contains many small vortex structures. To explore the influence of structures of different scales on the wake field, through the analysis of the modal energy distribution and the velocity field reconstruction results of Proper Orthogonal Decomposition (POD), it is found that there are different scale structures in the stern flow field, and the large-scale structure on the lower side of the propeller boss contributes more to the turbulent energy. As the normal position increases, the contribution of small scale structure to turbulence energy increases gradually.