PI-SiO2 hybrid seamless tubular films with gradient microstructure were prepared by sol-gel insitu polymerization and rotational moulding process. Energy Dispersive X-Ray Spectrometry (EDS) and Field Emitter Scanning Electron Microscope (FE-SEM) were used to evaluate the spatial gradient distribution of SiO2 in the PI-SiO2 hybrid tubular films. The experimental results showed that the SiO2 particles were dispersed at nanoscale in the PI matrix, and that the size and the dispersivity of the SiO2 particles changed gradiently along the tubular film cross-section. The lower the SiO2 distribution density, the smaller the SiO2 particles. When the SiO2 content exceeded a certain value, some SiO2 nano-particles aggregated into nano-clusters with thyrsiform structure, and the nano-clusters aggregated more into limbate globoids.