Abstract: To investigate the mesoscale structure characteristics of the middle-Stokes-number particle-laden jet (MSPJ) and the evolution law of scale-independent particle volume fraction, as well as to assess the applicability of a particle volume fraction model based on the self-similarity theory to MSPJ, we have established a specialized laser-camera measurement setup and conducted six groups of experiments. The characteristic scale and spatial scale-independent particle concentration are analyzed using the Voronoï method and the scale-independent particle cluster characterization method. The results indicate that the particle clusters in MSPJ exhibit a dynamic stability. As the Stokes number decreases from a large value to 1, the preferential concentration of particles becomes more pronounced. The long axis of the particle cluster serves as the primary characteristic size. Larger clusters display more irregular shapes, while smaller clusters appear to be circular and adhere to the power-law distribution described by the osmosis theory. The particle volume fraction of the jet reveals a distribution pattern characterized by a higher concentration at the center and lower concentrations at the edges. Along the jet centerline, the particle concentration initially decreases and then increases as one moves away from the nozzle. This phenomenon is attributed to the decay of particle velocity at the jet’s far end, where high-velocity particles from upstream catch up with lower-velocity particles downstream, leading to gradual accumulation. Validation of the particle volume fraction model demonstrates that the value of ηC_θ³ is influenced by turbulence. The particle distributions and clusters of different jets are self-similar. These findings provide a valuable foundation for enhancing the performance and efficiency of jet combustion systems.