The cassava starch as the research object, thermoplastic cassava starch (TPS)/silica (SiO2) composites were prepared by melt blending and molding methods. The effects of different particle sizes (0.02μm、0.2 μm、23 μm) silicon dioxide on the retrogradation melting enthalpy, retrogradation rate, retrogradation index, spherulite morphology, contact angle and thermal stability of thermoplastic cassava starch under ultrasound were studied. The results indicated that comparing with the non-ultrasonic sample, the differential scanning calorimetry (DSC) demonstrated that after ultrasonic treatment, the enthalpy of retrogradation of TPS/SiO2 composites increased, the retrogradation rate enhanced, and the retrogradation index decreased. The retrogradation rate of the product adding 20 nm SiO2 had the largest increase. Polarization (PLM) and water contact angle tests showed that TPS/SiO2 composite spherulite became obvious, and the contact angle increased. TG showed that the ultrasonic action made the moisture of the composite easy to volatilize, the binding ability of glycerol and starch increased, and the molecular structure stability of starch increased. SEM analysis indicated that the silica particles were less aggregated and better dispersed in the matrix under the action of ultrasound. The degree of retrogradation of the composite increased and the double helix structure decreased by FTIR analysis. XRD displayed that the composite presented A+V type crystal formed, and the V type crystal increased and the A type crystal reduced after ultrasonic treatment.