During the ultra-deep well drilling process, drilling fluid tends to remain in the casing, contaminating it and affecting the progress of completion engineering. To address this issue, a screening method was employed to select nonionic surfactants, with fatty alcohol polyoxyethylene ether (AEO-7) being chosen among various types. To overcome the temperature resistance issue of AEO-7, phthalic anhydride (PA) was introduced into AEO-7, and neutralization reaction with NaHCO3 was carried out to synthesize a novel surfactant (SEO). High-temperature and high-pressure precipitation testing equipment and high-temperature cleaning equipment were set up to study the temperature-resistant cleaning performance of SEO. Results indicate that surfactant SEO maintains good solubility in high-temperature environments in the solution through ionic bonding. At 200 °C, the cleaning efficiency of SEO solution for different types of drilling fluid residues exceeds 95 %. Additionally, SEO adsorption on metal surfaces can inhibit Cl- corrosion. Combined with micro-mechanism characterization results, SEO can disperse solid particles, adsorb organic phases, reduce interfacial tension, and achieve efficient cleaning. Field experimental results show that the surface tension retention rate of well-flushing fluid after cleaning is 95.8 %, with a solid particle content of 5.4 g/L, meeting onsite requirements and broad application prospects.