The invention provides a preparation method of a high speed engine base oil. The preparation method comprises following steps: pre-heating, hydroisomerization, hydrofining, high and low pressure separation, normal pressure distillation, pressure reduction fractional distillation, and secondary adsorption refining with a composite adsorbent. The preparation method is capable of changing oil molecular size, structure, and arrangement mode, increasing ideal components, inhibiting catalyst caking carbon deposition, reducing generation of nonideal components such as polycyclic aromatic hydrocarbonsand asphaltene, improving oil product quality, removing impurities, improving oil product chroma, flash point, and oxidation resistance, widening oil product application range, and improving stability obviously. The obtained high speed engine base oil is high in flash point, high in viscosity index, low in pour point, high in oxidation resistance, and high transmission efficiency, and can be usedfor high speed engines preferably.