Abstract: In order to improve the sealing ability of the annulus and ensure the multi-stage fracture-network fracturing development effect of tight oil horizontal wells in Yanchang Oilfield, the cement slurry had been functionally modified. Combined with the characteristics of tight oil reservoirs in the south part of this oilfield, horizontal well casing program and the requirements of multi-stage fracture-network fracturing on cement slurry properties, a casing-cement ring-formation force model was established, and the relationship chart between the Young’s modulus of the cement paste and the interfacial pressure was obtained. The particle size and surface treatment of styrene-butadiene rubber powder were optimized, and the high-strength micro-elastic agent was prepared by compounding formamide and inorganic salts, supplemented by other additives. After that, it was possible to form the high-strength micro-elastic cement slurry satisfying the requirements of this chart. The study found that the lower the Young's modulus of the hardened cement, the larger the Young's modulus of the formation, the lower the fracturing pressure and the smaller the hole enlargement rate, the lower the required compressive strength of the cement paste that met the requirements of annulus sealing would be. The developed cement slurry had perfect high-strength micro-elastic properties. Compared with the blank samples, the compressive strength was 51.8% higher, the Young's modulus was 10.5% lower, and the anti-breaking/tension strength was 75.0% higher. The cement slurry had been applied in more than 10 wells in the south part of the Yanchang Oilfield. The qualified rate of cementing quality in the horizontal section was over 95%, and no channeling occurred in the staged fracturing. The study results showed that the high-strength micro-elastic cement slurry could improve the post-fracturing sealing performance of tight oil horizontal wells in the Yanchang Oilfield, and demonstrated potential for widespread adoption.