Dendritic mesoporous nanomaterials (DMSNs) were prepared by a bicontinuous microemulsion method using tetraethyl orthosilicate (TEOS) and urea as raw materials, and Hexadecyl trimethyl ammonium bromide (CTAB) as a template. The effects of reaction time, TEOS addition (based on the percentage of p-xylene, the same below), co-solvent, stirring rate and reaction temperature on the morphology, particle size and pore size distribution of DMSNs were investigated by SEM, TEM, FTIR, XRD and N2 adsorption-desorption. The ability of DMSNs nanofluids to change rock wettability to improve oil recovery was explored. The competitive nucleation and growth mechanism during the formation of mesoporous nanomaterials was proposed to evaluate the wettability reversal effect of DMSNs. The results showed that the optimum conditions for the preparation of DMSNs were as follows: reaction time 6 h, TEOS addition amount 25%, ethylene glycol as co-solvent, stirring rate 1000 r / min and reaction temperature 85 °C. Under these conditions, the average particle size of DMSNs was 91 nm, the specific surface area was 1094.75 m2/g, the pore volume was 1.862 m3/g, and the average pore size was 6.1 nm. The surface of DMSNs has a special wrinkle morphology, showing a " flake / layered " flower-like mesoporous structure. The DMSNs nanofluid with 0.1% DMSNs content can change the wettability of rock from oil-wet to water-wet, and the contact angle increases from 0 ° to 132 °, which can effectively change the wettability of rock and significantly improve the tertiary oil recovery (39.6%). The competitive nucleation and growth mechanisms in the formation of DMSNs are three processes, namely initial nucleation, longitudinal growth, and secondary nucleation + lateral growth.